Issue 20804: Add java nullability annotations (#20806)

* issue-20804: Add nullability annotations to Java generated clients

Motivation:
Be able to use generated clients in code checked by tools like NullAway.

* issue-20804: Add nullability annotations to Java generated clients

Motivation:
Be able to use generated clients in code checked by tools like NullAway.

* issue-20804: Add nullability annotations to Java generated clients

Motivation:
Be able to use generated clients in code checked by tools like NullAway.

samples/client/petstore/java/feign/src/main/java/org/openapitools/client/api/AnotherFakeApi.java

@@ -27,7 +27,7 @@ public interface AnotherFakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  Client call123testSpecialTags(Client client);
+  Client call123testSpecialTags(@javax.annotation.Nonnull Client client);
 
   /**
    * To test special tags
@@ -41,7 +41,7 @@ public interface AnotherFakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Client> call123testSpecialTagsWithHttpInfo(Client client);
+  ApiResponse<Client> call123testSpecialTagsWithHttpInfo(@javax.annotation.Nonnull Client client);
 
 
 }

samples/client/petstore/java/feign/src/main/java/org/openapitools/client/api/FakeApi.java

@@ -93,7 +93,7 @@ public interface FakeApi extends ApiClient.Api {
     "Accept: application/json",
     "header_1: {header1}"
   })
-  void fakeHttpSignatureTest(Pet pet, @Param("query1") String query1, @Param("header1") String header1);
+  void fakeHttpSignatureTest(@javax.annotation.Nonnull Pet pet, @Param("query1") @javax.annotation.Nullable String query1, @Param("header1") @javax.annotation.Nullable String header1);
 
   /**
    * test http signature authentication
@@ -109,7 +109,7 @@ public interface FakeApi extends ApiClient.Api {
     "Accept: application/json",
     "header_1: {header1}"
   })
-  ApiResponse<Void> fakeHttpSignatureTestWithHttpInfo(Pet pet, @Param("query1") String query1, @Param("header1") String header1);
+  ApiResponse<Void> fakeHttpSignatureTestWithHttpInfo(@javax.annotation.Nonnull Pet pet, @Param("query1") @javax.annotation.Nullable String query1, @Param("header1") @javax.annotation.Nullable String header1);
 
 
   /**
@@ -134,7 +134,7 @@ public interface FakeApi extends ApiClient.Api {
   "Accept: application/json",
       "header_1: {header1}"
   })
-  void fakeHttpSignatureTest(Pet pet, @Param("header1") String header1, @QueryMap(encoded=true) FakeHttpSignatureTestQueryParams queryParams);
+  void fakeHttpSignatureTest(@javax.annotation.Nonnull Pet pet, @Param("header1") @javax.annotation.Nullable String header1, @QueryMap(encoded=true) FakeHttpSignatureTestQueryParams queryParams);
 
   /**
   * test http signature authentication
@@ -155,7 +155,7 @@ public interface FakeApi extends ApiClient.Api {
     "Accept: application/json",
           "header_1: {header1}"
       })
-   ApiResponse<Void> fakeHttpSignatureTestWithHttpInfo(Pet pet, @Param("header1") String header1, @QueryMap(encoded=true) FakeHttpSignatureTestQueryParams queryParams);
+   ApiResponse<Void> fakeHttpSignatureTestWithHttpInfo(@javax.annotation.Nonnull Pet pet, @Param("header1") @javax.annotation.Nullable String header1, @QueryMap(encoded=true) FakeHttpSignatureTestQueryParams queryParams);
 
 
    /**
@@ -163,7 +163,7 @@ public interface FakeApi extends ApiClient.Api {
    * <code>fakeHttpSignatureTest</code> method in a fluent style.
    */
   public static class FakeHttpSignatureTestQueryParams extends HashMap<String, Object> {
-    public FakeHttpSignatureTestQueryParams query1(final String value) {
+    public FakeHttpSignatureTestQueryParams query1(@javax.annotation.Nullable final String value) {
       put("query_1", EncodingUtils.encode(value));
       return this;
     }
@@ -180,7 +180,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  Boolean fakeOuterBooleanSerialize(Boolean body);
+  Boolean fakeOuterBooleanSerialize(@javax.annotation.Nullable Boolean body);
 
   /**
    * 
@@ -194,7 +194,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  ApiResponse<Boolean> fakeOuterBooleanSerializeWithHttpInfo(Boolean body);
+  ApiResponse<Boolean> fakeOuterBooleanSerializeWithHttpInfo(@javax.annotation.Nullable Boolean body);
 
 
 
@@ -209,7 +209,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  OuterComposite fakeOuterCompositeSerialize(OuterComposite outerComposite);
+  OuterComposite fakeOuterCompositeSerialize(@javax.annotation.Nullable OuterComposite outerComposite);
 
   /**
    * 
@@ -223,7 +223,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  ApiResponse<OuterComposite> fakeOuterCompositeSerializeWithHttpInfo(OuterComposite outerComposite);
+  ApiResponse<OuterComposite> fakeOuterCompositeSerializeWithHttpInfo(@javax.annotation.Nullable OuterComposite outerComposite);
 
 
 
@@ -238,7 +238,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  BigDecimal fakeOuterNumberSerialize(BigDecimal body);
+  BigDecimal fakeOuterNumberSerialize(@javax.annotation.Nullable BigDecimal body);
 
   /**
    * 
@@ -252,7 +252,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  ApiResponse<BigDecimal> fakeOuterNumberSerializeWithHttpInfo(BigDecimal body);
+  ApiResponse<BigDecimal> fakeOuterNumberSerializeWithHttpInfo(@javax.annotation.Nullable BigDecimal body);
 
 
 
@@ -267,7 +267,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  String fakeOuterStringSerialize(String body);
+  String fakeOuterStringSerialize(@javax.annotation.Nullable String body);
 
   /**
    * 
@@ -281,7 +281,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  ApiResponse<String> fakeOuterStringSerializeWithHttpInfo(String body);
+  ApiResponse<String> fakeOuterStringSerializeWithHttpInfo(@javax.annotation.Nullable String body);
 
 
 
@@ -296,7 +296,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  OuterObjectWithEnumProperty fakePropertyEnumIntegerSerialize(OuterObjectWithEnumProperty outerObjectWithEnumProperty);
+  OuterObjectWithEnumProperty fakePropertyEnumIntegerSerialize(@javax.annotation.Nonnull OuterObjectWithEnumProperty outerObjectWithEnumProperty);
 
   /**
    * 
@@ -310,7 +310,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: */*",
   })
-  ApiResponse<OuterObjectWithEnumProperty> fakePropertyEnumIntegerSerializeWithHttpInfo(OuterObjectWithEnumProperty outerObjectWithEnumProperty);
+  ApiResponse<OuterObjectWithEnumProperty> fakePropertyEnumIntegerSerializeWithHttpInfo(@javax.annotation.Nonnull OuterObjectWithEnumProperty outerObjectWithEnumProperty);
 
 
 
@@ -324,7 +324,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void testAdditionalPropertiesReference(Map<String, Object> requestBody);
+  void testAdditionalPropertiesReference(@javax.annotation.Nonnull Map<String, Object> requestBody);
 
   /**
    * test referenced additionalProperties
@@ -337,7 +337,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> testAdditionalPropertiesReferenceWithHttpInfo(Map<String, Object> requestBody);
+  ApiResponse<Void> testAdditionalPropertiesReferenceWithHttpInfo(@javax.annotation.Nonnull Map<String, Object> requestBody);
 
 
 
@@ -351,7 +351,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: image/png",
     "Accept: application/json",
   })
-  void testBodyWithBinary(File body);
+  void testBodyWithBinary(@javax.annotation.Nullable File body);
 
   /**
    * 
@@ -364,7 +364,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: image/png",
     "Accept: application/json",
   })
-  ApiResponse<Void> testBodyWithBinaryWithHttpInfo(File body);
+  ApiResponse<Void> testBodyWithBinaryWithHttpInfo(@javax.annotation.Nullable File body);
 
 
 
@@ -378,7 +378,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void testBodyWithFileSchema(FileSchemaTestClass fileSchemaTestClass);
+  void testBodyWithFileSchema(@javax.annotation.Nonnull FileSchemaTestClass fileSchemaTestClass);
 
   /**
    * 
@@ -391,7 +391,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> testBodyWithFileSchemaWithHttpInfo(FileSchemaTestClass fileSchemaTestClass);
+  ApiResponse<Void> testBodyWithFileSchemaWithHttpInfo(@javax.annotation.Nonnull FileSchemaTestClass fileSchemaTestClass);
 
 
 
@@ -406,7 +406,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void testBodyWithQueryParams(@Param("query") String query, User user);
+  void testBodyWithQueryParams(@Param("query") @javax.annotation.Nonnull String query, @javax.annotation.Nonnull User user);
 
   /**
    * 
@@ -420,7 +420,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> testBodyWithQueryParamsWithHttpInfo(@Param("query") String query, User user);
+  ApiResponse<Void> testBodyWithQueryParamsWithHttpInfo(@Param("query") @javax.annotation.Nonnull String query, @javax.annotation.Nonnull User user);
 
 
   /**
@@ -443,7 +443,7 @@ public interface FakeApi extends ApiClient.Api {
   "Content-Type: application/json",
   "Accept: application/json",
   })
-  void testBodyWithQueryParams(User user, @QueryMap(encoded=true) TestBodyWithQueryParamsQueryParams queryParams);
+  void testBodyWithQueryParams(@javax.annotation.Nonnull User user, @QueryMap(encoded=true) TestBodyWithQueryParamsQueryParams queryParams);
 
   /**
   * 
@@ -462,7 +462,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
       })
-   ApiResponse<Void> testBodyWithQueryParamsWithHttpInfo(User user, @QueryMap(encoded=true) TestBodyWithQueryParamsQueryParams queryParams);
+   ApiResponse<Void> testBodyWithQueryParamsWithHttpInfo(@javax.annotation.Nonnull User user, @QueryMap(encoded=true) TestBodyWithQueryParamsQueryParams queryParams);
 
 
    /**
@@ -470,7 +470,7 @@ public interface FakeApi extends ApiClient.Api {
    * <code>testBodyWithQueryParams</code> method in a fluent style.
    */
   public static class TestBodyWithQueryParamsQueryParams extends HashMap<String, Object> {
-    public TestBodyWithQueryParamsQueryParams query(final String value) {
+    public TestBodyWithQueryParamsQueryParams query(@javax.annotation.Nonnull final String value) {
       put("query", EncodingUtils.encode(value));
       return this;
     }
@@ -487,7 +487,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  Client testClientModel(Client client);
+  Client testClientModel(@javax.annotation.Nonnull Client client);
 
   /**
    * To test \&quot;client\&quot; model
@@ -501,7 +501,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Client> testClientModelWithHttpInfo(Client client);
+  ApiResponse<Client> testClientModelWithHttpInfo(@javax.annotation.Nonnull Client client);
 
 
 
@@ -528,7 +528,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/x-www-form-urlencoded",
     "Accept: application/json",
   })
-  void testEndpointParameters(@Param("number") BigDecimal number, @Param("double") Double _double, @Param("pattern_without_delimiter") String patternWithoutDelimiter, @Param("byte") byte[] _byte, @Param("integer") Integer integer, @Param("int32") Integer int32, @Param("int64") Long int64, @Param("float") Float _float, @Param("string") String string, @Param("binary") File binary, @Param("date") LocalDate date, @Param("dateTime") OffsetDateTime dateTime, @Param("password") String password, @Param("callback") String paramCallback);
+  void testEndpointParameters(@Param("number") @javax.annotation.Nonnull BigDecimal number, @Param("double") @javax.annotation.Nonnull Double _double, @Param("pattern_without_delimiter") @javax.annotation.Nonnull String patternWithoutDelimiter, @Param("byte") @javax.annotation.Nonnull byte[] _byte, @Param("integer") @javax.annotation.Nullable Integer integer, @Param("int32") @javax.annotation.Nullable Integer int32, @Param("int64") @javax.annotation.Nullable Long int64, @Param("float") @javax.annotation.Nullable Float _float, @Param("string") @javax.annotation.Nullable String string, @Param("binary") @javax.annotation.Nullable File binary, @Param("date") @javax.annotation.Nullable LocalDate date, @Param("dateTime") @javax.annotation.Nullable OffsetDateTime dateTime, @Param("password") @javax.annotation.Nullable String password, @Param("callback") @javax.annotation.Nullable String paramCallback);
 
   /**
    * Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
@@ -554,7 +554,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/x-www-form-urlencoded",
     "Accept: application/json",
   })
-  ApiResponse<Void> testEndpointParametersWithHttpInfo(@Param("number") BigDecimal number, @Param("double") Double _double, @Param("pattern_without_delimiter") String patternWithoutDelimiter, @Param("byte") byte[] _byte, @Param("integer") Integer integer, @Param("int32") Integer int32, @Param("int64") Long int64, @Param("float") Float _float, @Param("string") String string, @Param("binary") File binary, @Param("date") LocalDate date, @Param("dateTime") OffsetDateTime dateTime, @Param("password") String password, @Param("callback") String paramCallback);
+  ApiResponse<Void> testEndpointParametersWithHttpInfo(@Param("number") @javax.annotation.Nonnull BigDecimal number, @Param("double") @javax.annotation.Nonnull Double _double, @Param("pattern_without_delimiter") @javax.annotation.Nonnull String patternWithoutDelimiter, @Param("byte") @javax.annotation.Nonnull byte[] _byte, @Param("integer") @javax.annotation.Nullable Integer integer, @Param("int32") @javax.annotation.Nullable Integer int32, @Param("int64") @javax.annotation.Nullable Long int64, @Param("float") @javax.annotation.Nullable Float _float, @Param("string") @javax.annotation.Nullable String string, @Param("binary") @javax.annotation.Nullable File binary, @Param("date") @javax.annotation.Nullable LocalDate date, @Param("dateTime") @javax.annotation.Nullable OffsetDateTime dateTime, @Param("password") @javax.annotation.Nullable String password, @Param("callback") @javax.annotation.Nullable String paramCallback);
 
 
 
@@ -579,7 +579,7 @@ public interface FakeApi extends ApiClient.Api {
     
     "enum_header_string: {enumHeaderString}"
   })
-  void testEnumParameters(@Param("enumHeaderStringArray") List<String> enumHeaderStringArray, @Param("enumHeaderString") String enumHeaderString, @Param("enumQueryStringArray") List<String> enumQueryStringArray, @Param("enumQueryString") String enumQueryString, @Param("enumQueryInteger") Integer enumQueryInteger, @Param("enumQueryDouble") Double enumQueryDouble, @Param("enumQueryModelArray") List<EnumClass> enumQueryModelArray, @Param("enum_form_string_array") List<String> enumFormStringArray, @Param("enum_form_string") String enumFormString);
+  void testEnumParameters(@Param("enumHeaderStringArray") @javax.annotation.Nullable List<String> enumHeaderStringArray, @Param("enumHeaderString") @javax.annotation.Nullable String enumHeaderString, @Param("enumQueryStringArray") @javax.annotation.Nullable List<String> enumQueryStringArray, @Param("enumQueryString") @javax.annotation.Nullable String enumQueryString, @Param("enumQueryInteger") @javax.annotation.Nullable Integer enumQueryInteger, @Param("enumQueryDouble") @javax.annotation.Nullable Double enumQueryDouble, @Param("enumQueryModelArray") @javax.annotation.Nullable List<EnumClass> enumQueryModelArray, @Param("enum_form_string_array") @javax.annotation.Nullable List<String> enumFormStringArray, @Param("enum_form_string") @javax.annotation.Nullable String enumFormString);
 
   /**
    * To test enum parameters
@@ -603,7 +603,7 @@ public interface FakeApi extends ApiClient.Api {
     
     "enum_header_string: {enumHeaderString}"
   })
-  ApiResponse<Void> testEnumParametersWithHttpInfo(@Param("enumHeaderStringArray") List<String> enumHeaderStringArray, @Param("enumHeaderString") String enumHeaderString, @Param("enumQueryStringArray") List<String> enumQueryStringArray, @Param("enumQueryString") String enumQueryString, @Param("enumQueryInteger") Integer enumQueryInteger, @Param("enumQueryDouble") Double enumQueryDouble, @Param("enumQueryModelArray") List<EnumClass> enumQueryModelArray, @Param("enum_form_string_array") List<String> enumFormStringArray, @Param("enum_form_string") String enumFormString);
+  ApiResponse<Void> testEnumParametersWithHttpInfo(@Param("enumHeaderStringArray") @javax.annotation.Nullable List<String> enumHeaderStringArray, @Param("enumHeaderString") @javax.annotation.Nullable String enumHeaderString, @Param("enumQueryStringArray") @javax.annotation.Nullable List<String> enumQueryStringArray, @Param("enumQueryString") @javax.annotation.Nullable String enumQueryString, @Param("enumQueryInteger") @javax.annotation.Nullable Integer enumQueryInteger, @Param("enumQueryDouble") @javax.annotation.Nullable Double enumQueryDouble, @Param("enumQueryModelArray") @javax.annotation.Nullable List<EnumClass> enumQueryModelArray, @Param("enum_form_string_array") @javax.annotation.Nullable List<String> enumFormStringArray, @Param("enum_form_string") @javax.annotation.Nullable String enumFormString);
 
 
   /**
@@ -636,7 +636,7 @@ public interface FakeApi extends ApiClient.Api {
       
       "enum_header_string: {enumHeaderString}"
   })
-  void testEnumParameters(@Param("enumHeaderStringArray") List<String> enumHeaderStringArray, @Param("enumHeaderString") String enumHeaderString, @Param("enum_form_string_array") List<String> enumFormStringArray, @Param("enum_form_string") String enumFormString, @QueryMap(encoded=true) TestEnumParametersQueryParams queryParams);
+  void testEnumParameters(@Param("enumHeaderStringArray") @javax.annotation.Nullable List<String> enumHeaderStringArray, @Param("enumHeaderString") @javax.annotation.Nullable String enumHeaderString, @Param("enum_form_string_array") @javax.annotation.Nullable List<String> enumFormStringArray, @Param("enum_form_string") @javax.annotation.Nullable String enumFormString, @QueryMap(encoded=true) TestEnumParametersQueryParams queryParams);
 
   /**
   * To test enum parameters
@@ -665,7 +665,7 @@ public interface FakeApi extends ApiClient.Api {
       
           "enum_header_string: {enumHeaderString}"
       })
-   ApiResponse<Void> testEnumParametersWithHttpInfo(@Param("enumHeaderStringArray") List<String> enumHeaderStringArray, @Param("enumHeaderString") String enumHeaderString, @Param("enum_form_string_array") List<String> enumFormStringArray, @Param("enum_form_string") String enumFormString, @QueryMap(encoded=true) TestEnumParametersQueryParams queryParams);
+   ApiResponse<Void> testEnumParametersWithHttpInfo(@Param("enumHeaderStringArray") @javax.annotation.Nullable List<String> enumHeaderStringArray, @Param("enumHeaderString") @javax.annotation.Nullable String enumHeaderString, @Param("enum_form_string_array") @javax.annotation.Nullable List<String> enumFormStringArray, @Param("enum_form_string") @javax.annotation.Nullable String enumFormString, @QueryMap(encoded=true) TestEnumParametersQueryParams queryParams);
 
 
    /**
@@ -673,23 +673,23 @@ public interface FakeApi extends ApiClient.Api {
    * <code>testEnumParameters</code> method in a fluent style.
    */
   public static class TestEnumParametersQueryParams extends HashMap<String, Object> {
-    public TestEnumParametersQueryParams enumQueryStringArray(final List<String> value) {
+    public TestEnumParametersQueryParams enumQueryStringArray(@javax.annotation.Nullable final List<String> value) {
       put("enum_query_string_array", EncodingUtils.encodeCollection(value, "multi"));
       return this;
     }
-    public TestEnumParametersQueryParams enumQueryString(final String value) {
+    public TestEnumParametersQueryParams enumQueryString(@javax.annotation.Nullable final String value) {
       put("enum_query_string", EncodingUtils.encode(value));
       return this;
     }
-    public TestEnumParametersQueryParams enumQueryInteger(final Integer value) {
+    public TestEnumParametersQueryParams enumQueryInteger(@javax.annotation.Nullable final Integer value) {
       put("enum_query_integer", EncodingUtils.encode(value));
       return this;
     }
-    public TestEnumParametersQueryParams enumQueryDouble(final Double value) {
+    public TestEnumParametersQueryParams enumQueryDouble(@javax.annotation.Nullable final Double value) {
       put("enum_query_double", EncodingUtils.encode(value));
       return this;
     }
-    public TestEnumParametersQueryParams enumQueryModelArray(final List<EnumClass> value) {
+    public TestEnumParametersQueryParams enumQueryModelArray(@javax.annotation.Nullable final List<EnumClass> value) {
       put("enum_query_model_array", EncodingUtils.encodeCollection(value, "multi"));
       return this;
     }
@@ -712,7 +712,7 @@ public interface FakeApi extends ApiClient.Api {
     
     "boolean_group: {booleanGroup}"
   })
-  void testGroupParameters(@Param("requiredStringGroup") Integer requiredStringGroup, @Param("requiredBooleanGroup") Boolean requiredBooleanGroup, @Param("requiredInt64Group") Long requiredInt64Group, @Param("stringGroup") Integer stringGroup, @Param("booleanGroup") Boolean booleanGroup, @Param("int64Group") Long int64Group);
+  void testGroupParameters(@Param("requiredStringGroup") @javax.annotation.Nonnull Integer requiredStringGroup, @Param("requiredBooleanGroup") @javax.annotation.Nonnull Boolean requiredBooleanGroup, @Param("requiredInt64Group") @javax.annotation.Nonnull Long requiredInt64Group, @Param("stringGroup") @javax.annotation.Nullable Integer stringGroup, @Param("booleanGroup") @javax.annotation.Nullable Boolean booleanGroup, @Param("int64Group") @javax.annotation.Nullable Long int64Group);
 
   /**
    * Fake endpoint to test group parameters (optional)
@@ -732,7 +732,7 @@ public interface FakeApi extends ApiClient.Api {
     
     "boolean_group: {booleanGroup}"
   })
-  ApiResponse<Void> testGroupParametersWithHttpInfo(@Param("requiredStringGroup") Integer requiredStringGroup, @Param("requiredBooleanGroup") Boolean requiredBooleanGroup, @Param("requiredInt64Group") Long requiredInt64Group, @Param("stringGroup") Integer stringGroup, @Param("booleanGroup") Boolean booleanGroup, @Param("int64Group") Long int64Group);
+  ApiResponse<Void> testGroupParametersWithHttpInfo(@Param("requiredStringGroup") @javax.annotation.Nonnull Integer requiredStringGroup, @Param("requiredBooleanGroup") @javax.annotation.Nonnull Boolean requiredBooleanGroup, @Param("requiredInt64Group") @javax.annotation.Nonnull Long requiredInt64Group, @Param("stringGroup") @javax.annotation.Nullable Integer stringGroup, @Param("booleanGroup") @javax.annotation.Nullable Boolean booleanGroup, @Param("int64Group") @javax.annotation.Nullable Long int64Group);
 
 
   /**
@@ -761,7 +761,7 @@ public interface FakeApi extends ApiClient.Api {
       
       "boolean_group: {booleanGroup}"
   })
-  void testGroupParameters(@Param("requiredBooleanGroup") Boolean requiredBooleanGroup, @Param("booleanGroup") Boolean booleanGroup, @QueryMap(encoded=true) TestGroupParametersQueryParams queryParams);
+  void testGroupParameters(@Param("requiredBooleanGroup") @javax.annotation.Nonnull Boolean requiredBooleanGroup, @Param("booleanGroup") @javax.annotation.Nullable Boolean booleanGroup, @QueryMap(encoded=true) TestGroupParametersQueryParams queryParams);
 
   /**
   * Fake endpoint to test group parameters (optional)
@@ -786,7 +786,7 @@ public interface FakeApi extends ApiClient.Api {
       
           "boolean_group: {booleanGroup}"
       })
-   ApiResponse<Void> testGroupParametersWithHttpInfo(@Param("requiredBooleanGroup") Boolean requiredBooleanGroup, @Param("booleanGroup") Boolean booleanGroup, @QueryMap(encoded=true) TestGroupParametersQueryParams queryParams);
+   ApiResponse<Void> testGroupParametersWithHttpInfo(@Param("requiredBooleanGroup") @javax.annotation.Nonnull Boolean requiredBooleanGroup, @Param("booleanGroup") @javax.annotation.Nullable Boolean booleanGroup, @QueryMap(encoded=true) TestGroupParametersQueryParams queryParams);
 
 
    /**
@@ -794,19 +794,19 @@ public interface FakeApi extends ApiClient.Api {
    * <code>testGroupParameters</code> method in a fluent style.
    */
   public static class TestGroupParametersQueryParams extends HashMap<String, Object> {
-    public TestGroupParametersQueryParams requiredStringGroup(final Integer value) {
+    public TestGroupParametersQueryParams requiredStringGroup(@javax.annotation.Nonnull final Integer value) {
       put("required_string_group", EncodingUtils.encode(value));
       return this;
     }
-    public TestGroupParametersQueryParams requiredInt64Group(final Long value) {
+    public TestGroupParametersQueryParams requiredInt64Group(@javax.annotation.Nonnull final Long value) {
       put("required_int64_group", EncodingUtils.encode(value));
       return this;
     }
-    public TestGroupParametersQueryParams stringGroup(final Integer value) {
+    public TestGroupParametersQueryParams stringGroup(@javax.annotation.Nullable final Integer value) {
       put("string_group", EncodingUtils.encode(value));
       return this;
     }
-    public TestGroupParametersQueryParams int64Group(final Long value) {
+    public TestGroupParametersQueryParams int64Group(@javax.annotation.Nullable final Long value) {
       put("int64_group", EncodingUtils.encode(value));
       return this;
     }
@@ -822,7 +822,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void testInlineAdditionalProperties(Map<String, String> requestBody);
+  void testInlineAdditionalProperties(@javax.annotation.Nonnull Map<String, String> requestBody);
 
   /**
    * test inline additionalProperties
@@ -835,7 +835,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> testInlineAdditionalPropertiesWithHttpInfo(Map<String, String> requestBody);
+  ApiResponse<Void> testInlineAdditionalPropertiesWithHttpInfo(@javax.annotation.Nonnull Map<String, String> requestBody);
 
 
 
@@ -849,7 +849,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void testInlineFreeformAdditionalProperties(TestInlineFreeformAdditionalPropertiesRequest testInlineFreeformAdditionalPropertiesRequest);
+  void testInlineFreeformAdditionalProperties(@javax.annotation.Nonnull TestInlineFreeformAdditionalPropertiesRequest testInlineFreeformAdditionalPropertiesRequest);
 
   /**
    * test inline free-form additionalProperties
@@ -862,7 +862,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> testInlineFreeformAdditionalPropertiesWithHttpInfo(TestInlineFreeformAdditionalPropertiesRequest testInlineFreeformAdditionalPropertiesRequest);
+  ApiResponse<Void> testInlineFreeformAdditionalPropertiesWithHttpInfo(@javax.annotation.Nonnull TestInlineFreeformAdditionalPropertiesRequest testInlineFreeformAdditionalPropertiesRequest);
 
 
 
@@ -877,7 +877,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/x-www-form-urlencoded",
     "Accept: application/json",
   })
-  void testJsonFormData(@Param("param") String param, @Param("param2") String param2);
+  void testJsonFormData(@Param("param") @javax.annotation.Nonnull String param, @Param("param2") @javax.annotation.Nonnull String param2);
 
   /**
    * test json serialization of form data
@@ -891,7 +891,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/x-www-form-urlencoded",
     "Accept: application/json",
   })
-  ApiResponse<Void> testJsonFormDataWithHttpInfo(@Param("param") String param, @Param("param2") String param2);
+  ApiResponse<Void> testJsonFormDataWithHttpInfo(@Param("param") @javax.annotation.Nonnull String param, @Param("param2") @javax.annotation.Nonnull String param2);
 
 
 
@@ -905,7 +905,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void testNullable(ChildWithNullable childWithNullable);
+  void testNullable(@javax.annotation.Nonnull ChildWithNullable childWithNullable);
 
   /**
    * test nullable parent property
@@ -918,7 +918,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> testNullableWithHttpInfo(ChildWithNullable childWithNullable);
+  ApiResponse<Void> testNullableWithHttpInfo(@javax.annotation.Nonnull ChildWithNullable childWithNullable);
 
 
 
@@ -937,7 +937,7 @@ public interface FakeApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json",
   })
-  void testQueryParameterCollectionFormat(@Param("pipe") List<String> pipe, @Param("ioutil") List<String> ioutil, @Param("http") List<String> http, @Param("url") List<String> url, @Param("context") List<String> context, @Param("allowEmpty") String allowEmpty, @Param("language") Map<String, String> language);
+  void testQueryParameterCollectionFormat(@Param("pipe") @javax.annotation.Nonnull List<String> pipe, @Param("ioutil") @javax.annotation.Nonnull List<String> ioutil, @Param("http") @javax.annotation.Nonnull List<String> http, @Param("url") @javax.annotation.Nonnull List<String> url, @Param("context") @javax.annotation.Nonnull List<String> context, @Param("allowEmpty") @javax.annotation.Nonnull String allowEmpty, @Param("language") @javax.annotation.Nullable Map<String, String> language);
 
   /**
    * 
@@ -955,7 +955,7 @@ public interface FakeApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json",
   })
-  ApiResponse<Void> testQueryParameterCollectionFormatWithHttpInfo(@Param("pipe") List<String> pipe, @Param("ioutil") List<String> ioutil, @Param("http") List<String> http, @Param("url") List<String> url, @Param("context") List<String> context, @Param("allowEmpty") String allowEmpty, @Param("language") Map<String, String> language);
+  ApiResponse<Void> testQueryParameterCollectionFormatWithHttpInfo(@Param("pipe") @javax.annotation.Nonnull List<String> pipe, @Param("ioutil") @javax.annotation.Nonnull List<String> ioutil, @Param("http") @javax.annotation.Nonnull List<String> http, @Param("url") @javax.annotation.Nonnull List<String> url, @Param("context") @javax.annotation.Nonnull List<String> context, @Param("allowEmpty") @javax.annotation.Nonnull String allowEmpty, @Param("language") @javax.annotation.Nullable Map<String, String> language);
 
 
   /**
@@ -1013,31 +1013,31 @@ public interface FakeApi extends ApiClient.Api {
    * <code>testQueryParameterCollectionFormat</code> method in a fluent style.
    */
   public static class TestQueryParameterCollectionFormatQueryParams extends HashMap<String, Object> {
-    public TestQueryParameterCollectionFormatQueryParams pipe(final List<String> value) {
+    public TestQueryParameterCollectionFormatQueryParams pipe(@javax.annotation.Nonnull final List<String> value) {
       put("pipe", EncodingUtils.encodeCollection(value, "pipes"));
       return this;
     }
-    public TestQueryParameterCollectionFormatQueryParams ioutil(final List<String> value) {
+    public TestQueryParameterCollectionFormatQueryParams ioutil(@javax.annotation.Nonnull final List<String> value) {
       put("ioutil", EncodingUtils.encodeCollection(value, "csv"));
       return this;
     }
-    public TestQueryParameterCollectionFormatQueryParams http(final List<String> value) {
+    public TestQueryParameterCollectionFormatQueryParams http(@javax.annotation.Nonnull final List<String> value) {
       put("http", EncodingUtils.encodeCollection(value, "ssv"));
       return this;
     }
-    public TestQueryParameterCollectionFormatQueryParams url(final List<String> value) {
+    public TestQueryParameterCollectionFormatQueryParams url(@javax.annotation.Nonnull final List<String> value) {
       put("url", EncodingUtils.encodeCollection(value, "csv"));
       return this;
     }
-    public TestQueryParameterCollectionFormatQueryParams context(final List<String> value) {
+    public TestQueryParameterCollectionFormatQueryParams context(@javax.annotation.Nonnull final List<String> value) {
       put("context", EncodingUtils.encodeCollection(value, "multi"));
       return this;
     }
-    public TestQueryParameterCollectionFormatQueryParams language(final Map<String, String> value) {
+    public TestQueryParameterCollectionFormatQueryParams language(@javax.annotation.Nullable final Map<String, String> value) {
       put("language", EncodingUtils.encode(value));
       return this;
     }
-    public TestQueryParameterCollectionFormatQueryParams allowEmpty(final String value) {
+    public TestQueryParameterCollectionFormatQueryParams allowEmpty(@javax.annotation.Nonnull final String value) {
       put("allowEmpty", EncodingUtils.encode(value));
       return this;
     }
@@ -1053,7 +1053,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void testStringMapReference(Map<String, String> requestBody);
+  void testStringMapReference(@javax.annotation.Nonnull Map<String, String> requestBody);
 
   /**
    * test referenced string map
@@ -1066,7 +1066,7 @@ public interface FakeApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> testStringMapReferenceWithHttpInfo(Map<String, String> requestBody);
+  ApiResponse<Void> testStringMapReferenceWithHttpInfo(@javax.annotation.Nonnull Map<String, String> requestBody);
 
 
 }

samples/client/petstore/java/feign/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java

@@ -27,7 +27,7 @@ public interface FakeClassnameTags123Api extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  Client testClassname(Client client);
+  Client testClassname(@javax.annotation.Nonnull Client client);
 
   /**
    * To test class name in snake case
@@ -41,7 +41,7 @@ public interface FakeClassnameTags123Api extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Client> testClassnameWithHttpInfo(Client client);
+  ApiResponse<Client> testClassnameWithHttpInfo(@javax.annotation.Nonnull Client client);
 
 
 }

samples/client/petstore/java/feign/src/main/java/org/openapitools/client/api/PetApi.java

@@ -29,7 +29,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void addPet(Pet pet);
+  void addPet(@javax.annotation.Nonnull Pet pet);
 
   /**
    * Add a new pet to the store
@@ -42,7 +42,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> addPetWithHttpInfo(Pet pet);
+  ApiResponse<Void> addPetWithHttpInfo(@javax.annotation.Nonnull Pet pet);
 
 
 
@@ -57,7 +57,7 @@ public interface PetApi extends ApiClient.Api {
     "Accept: application/json",
     "api_key: {apiKey}"
   })
-  void deletePet(@Param("petId") Long petId, @Param("apiKey") String apiKey);
+  void deletePet(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("apiKey") @javax.annotation.Nullable String apiKey);
 
   /**
    * Deletes a pet
@@ -71,7 +71,7 @@ public interface PetApi extends ApiClient.Api {
     "Accept: application/json",
     "api_key: {apiKey}"
   })
-  ApiResponse<Void> deletePetWithHttpInfo(@Param("petId") Long petId, @Param("apiKey") String apiKey);
+  ApiResponse<Void> deletePetWithHttpInfo(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("apiKey") @javax.annotation.Nullable String apiKey);
 
 
 
@@ -85,7 +85,7 @@ public interface PetApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  List<Pet> findPetsByStatus(@Param("status") List<String> status);
+  List<Pet> findPetsByStatus(@Param("status") @javax.annotation.Nonnull List<String> status);
 
   /**
    * Finds Pets by status
@@ -98,7 +98,7 @@ public interface PetApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  ApiResponse<List<Pet>> findPetsByStatusWithHttpInfo(@Param("status") List<String> status);
+  ApiResponse<List<Pet>> findPetsByStatusWithHttpInfo(@Param("status") @javax.annotation.Nonnull List<String> status);
 
 
   /**
@@ -146,7 +146,7 @@ public interface PetApi extends ApiClient.Api {
    * <code>findPetsByStatus</code> method in a fluent style.
    */
   public static class FindPetsByStatusQueryParams extends HashMap<String, Object> {
-    public FindPetsByStatusQueryParams status(final List<String> value) {
+    public FindPetsByStatusQueryParams status(@javax.annotation.Nonnull final List<String> value) {
       put("status", EncodingUtils.encodeCollection(value, "csv"));
       return this;
     }
@@ -164,7 +164,7 @@ public interface PetApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  Set<Pet> findPetsByTags(@Param("tags") Set<String> tags);
+  Set<Pet> findPetsByTags(@Param("tags") @javax.annotation.Nonnull Set<String> tags);
 
   /**
    * Finds Pets by tags
@@ -179,7 +179,7 @@ public interface PetApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  ApiResponse<Set<Pet>> findPetsByTagsWithHttpInfo(@Param("tags") Set<String> tags);
+  ApiResponse<Set<Pet>> findPetsByTagsWithHttpInfo(@Param("tags") @javax.annotation.Nonnull Set<String> tags);
 
 
   /**
@@ -231,7 +231,7 @@ public interface PetApi extends ApiClient.Api {
    * <code>findPetsByTags</code> method in a fluent style.
    */
   public static class FindPetsByTagsQueryParams extends HashMap<String, Object> {
-    public FindPetsByTagsQueryParams tags(final Set<String> value) {
+    public FindPetsByTagsQueryParams tags(@javax.annotation.Nonnull final Set<String> value) {
       put("tags", EncodingUtils.encodeCollection(value, "csv"));
       return this;
     }
@@ -247,7 +247,7 @@ public interface PetApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  Pet getPetById(@Param("petId") Long petId);
+  Pet getPetById(@Param("petId") @javax.annotation.Nonnull Long petId);
 
   /**
    * Find pet by ID
@@ -260,7 +260,7 @@ public interface PetApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  ApiResponse<Pet> getPetByIdWithHttpInfo(@Param("petId") Long petId);
+  ApiResponse<Pet> getPetByIdWithHttpInfo(@Param("petId") @javax.annotation.Nonnull Long petId);
 
 
 
@@ -274,7 +274,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void updatePet(Pet pet);
+  void updatePet(@javax.annotation.Nonnull Pet pet);
 
   /**
    * Update an existing pet
@@ -287,7 +287,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> updatePetWithHttpInfo(Pet pet);
+  ApiResponse<Void> updatePetWithHttpInfo(@javax.annotation.Nonnull Pet pet);
 
 
 
@@ -303,7 +303,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: application/x-www-form-urlencoded",
     "Accept: application/json",
   })
-  void updatePetWithForm(@Param("petId") Long petId, @Param("name") String name, @Param("status") String status);
+  void updatePetWithForm(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("name") @javax.annotation.Nullable String name, @Param("status") @javax.annotation.Nullable String status);
 
   /**
    * Updates a pet in the store with form data
@@ -318,7 +318,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: application/x-www-form-urlencoded",
     "Accept: application/json",
   })
-  ApiResponse<Void> updatePetWithFormWithHttpInfo(@Param("petId") Long petId, @Param("name") String name, @Param("status") String status);
+  ApiResponse<Void> updatePetWithFormWithHttpInfo(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("name") @javax.annotation.Nullable String name, @Param("status") @javax.annotation.Nullable String status);
 
 
 
@@ -335,7 +335,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: multipart/form-data",
     "Accept: application/json",
   })
-  ModelApiResponse uploadFile(@Param("petId") Long petId, @Param("additionalMetadata") String additionalMetadata, @Param("file") File file);
+  ModelApiResponse uploadFile(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("additionalMetadata") @javax.annotation.Nullable String additionalMetadata, @Param("file") @javax.annotation.Nullable File file);
 
   /**
    * uploads an image
@@ -351,7 +351,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: multipart/form-data",
     "Accept: application/json",
   })
-  ApiResponse<ModelApiResponse> uploadFileWithHttpInfo(@Param("petId") Long petId, @Param("additionalMetadata") String additionalMetadata, @Param("file") File file);
+  ApiResponse<ModelApiResponse> uploadFileWithHttpInfo(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("additionalMetadata") @javax.annotation.Nullable String additionalMetadata, @Param("file") @javax.annotation.Nullable File file);
 
 
 
@@ -368,7 +368,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: multipart/form-data",
     "Accept: application/json",
   })
-  ModelApiResponse uploadFileWithRequiredFile(@Param("petId") Long petId, @Param("requiredFile") File requiredFile, @Param("additionalMetadata") String additionalMetadata);
+  ModelApiResponse uploadFileWithRequiredFile(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("requiredFile") @javax.annotation.Nonnull File requiredFile, @Param("additionalMetadata") @javax.annotation.Nullable String additionalMetadata);
 
   /**
    * uploads an image (required)
@@ -384,7 +384,7 @@ public interface PetApi extends ApiClient.Api {
     "Content-Type: multipart/form-data",
     "Accept: application/json",
   })
-  ApiResponse<ModelApiResponse> uploadFileWithRequiredFileWithHttpInfo(@Param("petId") Long petId, @Param("requiredFile") File requiredFile, @Param("additionalMetadata") String additionalMetadata);
+  ApiResponse<ModelApiResponse> uploadFileWithRequiredFileWithHttpInfo(@Param("petId") @javax.annotation.Nonnull Long petId, @Param("requiredFile") @javax.annotation.Nonnull File requiredFile, @Param("additionalMetadata") @javax.annotation.Nullable String additionalMetadata);
 
 
 }

samples/client/petstore/java/feign/src/main/java/org/openapitools/client/api/StoreApi.java

@@ -25,7 +25,7 @@ public interface StoreApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json",
   })
-  void deleteOrder(@Param("orderId") String orderId);
+  void deleteOrder(@Param("orderId") @javax.annotation.Nonnull String orderId);
 
   /**
    * Delete purchase order by ID
@@ -37,7 +37,7 @@ public interface StoreApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json",
   })
-  ApiResponse<Void> deleteOrderWithHttpInfo(@Param("orderId") String orderId);
+  ApiResponse<Void> deleteOrderWithHttpInfo(@Param("orderId") @javax.annotation.Nonnull String orderId);
 
 
 
@@ -76,7 +76,7 @@ public interface StoreApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  Order getOrderById(@Param("orderId") Long orderId);
+  Order getOrderById(@Param("orderId") @javax.annotation.Nonnull Long orderId);
 
   /**
    * Find purchase order by ID
@@ -89,7 +89,7 @@ public interface StoreApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  ApiResponse<Order> getOrderByIdWithHttpInfo(@Param("orderId") Long orderId);
+  ApiResponse<Order> getOrderByIdWithHttpInfo(@Param("orderId") @javax.annotation.Nonnull Long orderId);
 
 
 
@@ -104,7 +104,7 @@ public interface StoreApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json,application/xml",
   })
-  Order placeOrder(Order order);
+  Order placeOrder(@javax.annotation.Nonnull Order order);
 
   /**
    * Place an order for a pet
@@ -118,7 +118,7 @@ public interface StoreApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json,application/xml",
   })
-  ApiResponse<Order> placeOrderWithHttpInfo(Order order);
+  ApiResponse<Order> placeOrderWithHttpInfo(@javax.annotation.Nonnull Order order);
 
 
 }

samples/client/petstore/java/feign/src/main/java/org/openapitools/client/api/UserApi.java

@@ -27,7 +27,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void createUser(User user);
+  void createUser(@javax.annotation.Nonnull User user);
 
   /**
    * Create user
@@ -40,7 +40,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> createUserWithHttpInfo(User user);
+  ApiResponse<Void> createUserWithHttpInfo(@javax.annotation.Nonnull User user);
 
 
 
@@ -54,7 +54,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void createUsersWithArrayInput(List<User> user);
+  void createUsersWithArrayInput(@javax.annotation.Nonnull List<User> user);
 
   /**
    * Creates list of users with given input array
@@ -67,7 +67,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> createUsersWithArrayInputWithHttpInfo(List<User> user);
+  ApiResponse<Void> createUsersWithArrayInputWithHttpInfo(@javax.annotation.Nonnull List<User> user);
 
 
 
@@ -81,7 +81,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void createUsersWithListInput(List<User> user);
+  void createUsersWithListInput(@javax.annotation.Nonnull List<User> user);
 
   /**
    * Creates list of users with given input array
@@ -94,7 +94,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> createUsersWithListInputWithHttpInfo(List<User> user);
+  ApiResponse<Void> createUsersWithListInputWithHttpInfo(@javax.annotation.Nonnull List<User> user);
 
 
 
@@ -107,7 +107,7 @@ public interface UserApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json",
   })
-  void deleteUser(@Param("username") String username);
+  void deleteUser(@Param("username") @javax.annotation.Nonnull String username);
 
   /**
    * Delete user
@@ -119,7 +119,7 @@ public interface UserApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json",
   })
-  ApiResponse<Void> deleteUserWithHttpInfo(@Param("username") String username);
+  ApiResponse<Void> deleteUserWithHttpInfo(@Param("username") @javax.annotation.Nonnull String username);
 
 
 
@@ -133,7 +133,7 @@ public interface UserApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  User getUserByName(@Param("username") String username);
+  User getUserByName(@Param("username") @javax.annotation.Nonnull String username);
 
   /**
    * Get user by user name
@@ -146,7 +146,7 @@ public interface UserApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  ApiResponse<User> getUserByNameWithHttpInfo(@Param("username") String username);
+  ApiResponse<User> getUserByNameWithHttpInfo(@Param("username") @javax.annotation.Nonnull String username);
 
 
 
@@ -161,7 +161,7 @@ public interface UserApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  String loginUser(@Param("username") String username, @Param("password") String password);
+  String loginUser(@Param("username") @javax.annotation.Nonnull String username, @Param("password") @javax.annotation.Nonnull String password);
 
   /**
    * Logs user into the system
@@ -175,7 +175,7 @@ public interface UserApi extends ApiClient.Api {
   @Headers({
     "Accept: application/json,application/xml",
   })
-  ApiResponse<String> loginUserWithHttpInfo(@Param("username") String username, @Param("password") String password);
+  ApiResponse<String> loginUserWithHttpInfo(@Param("username") @javax.annotation.Nonnull String username, @Param("password") @javax.annotation.Nonnull String password);
 
 
   /**
@@ -225,11 +225,11 @@ public interface UserApi extends ApiClient.Api {
    * <code>loginUser</code> method in a fluent style.
    */
   public static class LoginUserQueryParams extends HashMap<String, Object> {
-    public LoginUserQueryParams username(final String value) {
+    public LoginUserQueryParams username(@javax.annotation.Nonnull final String value) {
       put("username", EncodingUtils.encode(value));
       return this;
     }
-    public LoginUserQueryParams password(final String value) {
+    public LoginUserQueryParams password(@javax.annotation.Nonnull final String value) {
       put("password", EncodingUtils.encode(value));
       return this;
     }
@@ -269,7 +269,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  void updateUser(@Param("username") String username, User user);
+  void updateUser(@Param("username") @javax.annotation.Nonnull String username, @javax.annotation.Nonnull User user);
 
   /**
    * Updated user
@@ -283,7 +283,7 @@ public interface UserApi extends ApiClient.Api {
     "Content-Type: application/json",
     "Accept: application/json",
   })
-  ApiResponse<Void> updateUserWithHttpInfo(@Param("username") String username, User user);
+  ApiResponse<Void> updateUserWithHttpInfo(@Param("username") @javax.annotation.Nonnull String username, @javax.annotation.Nonnull User user);
 
 
 }