diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
index 604bce325eb..a95e21cb0cf 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java
@@ -3506,7 +3506,10 @@ public class DefaultCodegen implements CodegenConfig {
         if (Boolean.FALSE.equals(p.getNullable())) {
             LOGGER.warn("Schema '{}' is any type, which includes the 'null' value. 'nullable' cannot be set to 'false'", p.getName());
         }
-        property.isNullable = true;
+        ComposedSchema composedSchema = p instanceof ComposedSchema
+            ? (ComposedSchema) p
+            : null;
+        property.isNullable = property.isNullable || composedSchema == null || composedSchema.getAllOf() == null || composedSchema.getAllOf().size() == 0;
         if (languageSpecificPrimitives.contains(property.dataType)) {
             property.isPrimitiveType = true;
         }
diff --git a/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Model/AllOfWithSingleRef.cs b/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Model/AllOfWithSingleRef.cs
index dcd135e949d..1cce653b433 100644
--- a/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Model/AllOfWithSingleRef.cs
+++ b/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Model/AllOfWithSingleRef.cs
@@ -33,7 +33,7 @@ namespace Org.OpenAPITools.Model
         /// <summary>
         /// Gets or Sets SingleRefType
         /// </summary>
-        [DataMember(Name="SingleRefType", EmitDefaultValue=true)]
+        [DataMember(Name="SingleRefType", EmitDefaultValue=false)]
         public SingleRefType? SingleRefType { get; set; }
         /// <summary>
         /// Initializes a new instance of the <see cref="AllOfWithSingleRef" /> class.
@@ -42,7 +42,6 @@ namespace Org.OpenAPITools.Model
         /// <param name="singleRefType">singleRefType.</param>
         public AllOfWithSingleRef(string username = default(string), SingleRefType? singleRefType = default(SingleRefType?))
         {
-            this.SingleRefType = singleRefType;
             this.Username = username;
             this.SingleRefType = singleRefType;
         }
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java
index da5ebd59abd..485e4517736 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java
@@ -23,10 +23,6 @@ import com.fasterxml.jackson.annotation.JsonValue;
 import io.swagger.annotations.ApiModel;
 import io.swagger.annotations.ApiModelProperty;
 import org.openapitools.client.model.SingleRefType;
-import org.openapitools.jackson.nullable.JsonNullable;
-import com.fasterxml.jackson.annotation.JsonIgnore;
-import org.openapitools.jackson.nullable.JsonNullable;
-import java.util.NoSuchElementException;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 import com.fasterxml.jackson.annotation.JsonTypeName;
 
@@ -43,7 +39,7 @@ public class AllOfWithSingleRef {
   private String username;
 
   public static final String JSON_PROPERTY_SINGLE_REF_TYPE = "SingleRefType";
-  private JsonNullable<SingleRefType> singleRefType = JsonNullable.<SingleRefType>undefined();
+  private SingleRefType singleRefType;
 
   public AllOfWithSingleRef() {
   }
@@ -76,8 +72,8 @@ public class AllOfWithSingleRef {
 
 
   public AllOfWithSingleRef singleRefType(SingleRefType singleRefType) {
-    this.singleRefType = JsonNullable.<SingleRefType>of(singleRefType);
     
+    this.singleRefType = singleRefType;
     return this;
   }
 
@@ -87,26 +83,18 @@ public class AllOfWithSingleRef {
   **/
   @javax.annotation.Nullable
   @ApiModelProperty(value = "")
-  @JsonIgnore
-
-  public SingleRefType getSingleRefType() {
-        return singleRefType.orElse(null);
-  }
-
   @JsonProperty(JSON_PROPERTY_SINGLE_REF_TYPE)
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
 
-  public JsonNullable<SingleRefType> getSingleRefType_JsonNullable() {
+  public SingleRefType getSingleRefType() {
     return singleRefType;
   }
-  
-  @JsonProperty(JSON_PROPERTY_SINGLE_REF_TYPE)
-  public void setSingleRefType_JsonNullable(JsonNullable<SingleRefType> singleRefType) {
-    this.singleRefType = singleRefType;
-  }
 
+
+  @JsonProperty(JSON_PROPERTY_SINGLE_REF_TYPE)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
   public void setSingleRefType(SingleRefType singleRefType) {
-    this.singleRefType = JsonNullable.<SingleRefType>of(singleRefType);
+    this.singleRefType = singleRefType;
   }
 
 
@@ -120,23 +108,12 @@ public class AllOfWithSingleRef {
     }
     AllOfWithSingleRef allOfWithSingleRef = (AllOfWithSingleRef) o;
     return Objects.equals(this.username, allOfWithSingleRef.username) &&
-        equalsNullable(this.singleRefType, allOfWithSingleRef.singleRefType);
-  }
-
-  private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
-    return a == b || (a != null && b != null && a.isPresent() && b.isPresent() && Objects.deepEquals(a.get(), b.get()));
+        Objects.equals(this.singleRefType, allOfWithSingleRef.singleRefType);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(username, hashCodeNullable(singleRefType));
-  }
-
-  private static <T> int hashCodeNullable(JsonNullable<T> a) {
-    if (a == null) {
-      return 1;
-    }
-    return a.isPresent() ? Arrays.deepHashCode(new Object[]{a.get()}) : 31;
+    return Objects.hash(username, singleRefType);
   }
 
   @Override
diff --git a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java
index da5ebd59abd..485e4517736 100644
--- a/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java
+++ b/samples/client/petstore/java/webclient/src/main/java/org/openapitools/client/model/AllOfWithSingleRef.java
@@ -23,10 +23,6 @@ import com.fasterxml.jackson.annotation.JsonValue;
 import io.swagger.annotations.ApiModel;
 import io.swagger.annotations.ApiModelProperty;
 import org.openapitools.client.model.SingleRefType;
-import org.openapitools.jackson.nullable.JsonNullable;
-import com.fasterxml.jackson.annotation.JsonIgnore;
-import org.openapitools.jackson.nullable.JsonNullable;
-import java.util.NoSuchElementException;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 import com.fasterxml.jackson.annotation.JsonTypeName;
 
@@ -43,7 +39,7 @@ public class AllOfWithSingleRef {
   private String username;
 
   public static final String JSON_PROPERTY_SINGLE_REF_TYPE = "SingleRefType";
-  private JsonNullable<SingleRefType> singleRefType = JsonNullable.<SingleRefType>undefined();
+  private SingleRefType singleRefType;
 
   public AllOfWithSingleRef() {
   }
@@ -76,8 +72,8 @@ public class AllOfWithSingleRef {
 
 
   public AllOfWithSingleRef singleRefType(SingleRefType singleRefType) {
-    this.singleRefType = JsonNullable.<SingleRefType>of(singleRefType);
     
+    this.singleRefType = singleRefType;
     return this;
   }
 
@@ -87,26 +83,18 @@ public class AllOfWithSingleRef {
   **/
   @javax.annotation.Nullable
   @ApiModelProperty(value = "")
-  @JsonIgnore
-
-  public SingleRefType getSingleRefType() {
-        return singleRefType.orElse(null);
-  }
-
   @JsonProperty(JSON_PROPERTY_SINGLE_REF_TYPE)
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
 
-  public JsonNullable<SingleRefType> getSingleRefType_JsonNullable() {
+  public SingleRefType getSingleRefType() {
     return singleRefType;
   }
-  
-  @JsonProperty(JSON_PROPERTY_SINGLE_REF_TYPE)
-  public void setSingleRefType_JsonNullable(JsonNullable<SingleRefType> singleRefType) {
-    this.singleRefType = singleRefType;
-  }
 
+
+  @JsonProperty(JSON_PROPERTY_SINGLE_REF_TYPE)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
   public void setSingleRefType(SingleRefType singleRefType) {
-    this.singleRefType = JsonNullable.<SingleRefType>of(singleRefType);
+    this.singleRefType = singleRefType;
   }
 
 
@@ -120,23 +108,12 @@ public class AllOfWithSingleRef {
     }
     AllOfWithSingleRef allOfWithSingleRef = (AllOfWithSingleRef) o;
     return Objects.equals(this.username, allOfWithSingleRef.username) &&
-        equalsNullable(this.singleRefType, allOfWithSingleRef.singleRefType);
-  }
-
-  private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
-    return a == b || (a != null && b != null && a.isPresent() && b.isPresent() && Objects.deepEquals(a.get(), b.get()));
+        Objects.equals(this.singleRefType, allOfWithSingleRef.singleRefType);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(username, hashCodeNullable(singleRefType));
-  }
-
-  private static <T> int hashCodeNullable(JsonNullable<T> a) {
-    if (a == null) {
-      return 1;
-    }
-    return a.isPresent() ? Arrays.deepHashCode(new Object[]{a.get()}) : 31;
+    return Objects.hash(username, singleRefType);
   }
 
   @Override
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php
index 3c6fa68e2bf..3c7e762495f 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php
@@ -80,7 +80,7 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, \JsonSerializab
       */
     protected static array $openAPINullables = [
         'username' => false,
-		'single_ref_type' => true
+		'single_ref_type' => false
     ];
 
     /**
@@ -336,14 +336,7 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, \JsonSerializab
     {
 
         if (is_null($single_ref_type)) {
-            array_push($this->openAPINullablesSetToNull, 'single_ref_type');
-        } else {
-            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
-            $index = array_search('single_ref_type', $nullablesSetToNull);
-            if ($index !== FALSE) {
-                unset($nullablesSetToNull[$index]);
-                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
-            }
+            throw new \InvalidArgumentException('non-nullable single_ref_type cannot be null');
         }
 
         $this->container['single_ref_type'] = $single_ref_type;
diff --git a/samples/client/petstore/ruby-faraday/lib/petstore/models/all_of_with_single_ref.rb b/samples/client/petstore/ruby-faraday/lib/petstore/models/all_of_with_single_ref.rb
index 4efc82eac4a..89884ca12b0 100644
--- a/samples/client/petstore/ruby-faraday/lib/petstore/models/all_of_with_single_ref.rb
+++ b/samples/client/petstore/ruby-faraday/lib/petstore/models/all_of_with_single_ref.rb
@@ -43,7 +43,6 @@ module Petstore
     # List of attributes with nullable: true
     def self.openapi_nullable
       Set.new([
-        :'single_ref_type'
       ])
     end
 
diff --git a/samples/client/petstore/ruby/lib/petstore/models/all_of_with_single_ref.rb b/samples/client/petstore/ruby/lib/petstore/models/all_of_with_single_ref.rb
index 4efc82eac4a..89884ca12b0 100644
--- a/samples/client/petstore/ruby/lib/petstore/models/all_of_with_single_ref.rb
+++ b/samples/client/petstore/ruby/lib/petstore/models/all_of_with_single_ref.rb
@@ -43,7 +43,6 @@ module Petstore
     # List of attributes with nullable: true
     def self.openapi_nullable
       Set.new([
-        :'single_ref_type'
       ])
     end
 
diff --git a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/AllOfWithSingleRef.ts b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/AllOfWithSingleRef.ts
index 61f2a287c80..13958e2ab77 100644
--- a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/AllOfWithSingleRef.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/AllOfWithSingleRef.ts
@@ -37,7 +37,7 @@ export interface AllOfWithSingleRef {
      * @type {SingleRefType}
      * @memberof AllOfWithSingleRef
      */
-    singleRefType?: SingleRefType | null;
+    singleRefType?: SingleRefType;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/model/all_of_with_single_ref.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/model/all_of_with_single_ref.dart
index 460aec9a9c8..7ee9944f7f0 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/model/all_of_with_single_ref.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/model/all_of_with_single_ref.dart
@@ -55,7 +55,7 @@ class AllOfWithSingleRef {
   @override
   int get hashCode =>
     username.hashCode +
-    (singleRefType == null ? 0 : singleRefType.hashCode);
+    singleRefType.hashCode;
 
   factory AllOfWithSingleRef.fromJson(Map<String, dynamic> json) => _$AllOfWithSingleRefFromJson(json);
 
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/model/all_of_with_single_ref.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/model/all_of_with_single_ref.dart
index 3319d53814d..a6955be4a92 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/model/all_of_with_single_ref.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/model/all_of_with_single_ref.dart
@@ -52,7 +52,7 @@ class _$AllOfWithSingleRefSerializer implements StructuredSerializer<AllOfWithSi
             result
                 ..add(r'SingleRefType')
                 ..add(serializers.serialize(object.singleRefType,
-                    specifiedType: const FullType.nullable(SingleRefType)));
+                    specifiedType: const FullType(SingleRefType)));
         }
         return result;
     }
@@ -76,8 +76,7 @@ class _$AllOfWithSingleRefSerializer implements StructuredSerializer<AllOfWithSi
                     break;
                 case r'SingleRefType':
                     final valueDes = serializers.deserialize(value,
-                        specifiedType: const FullType.nullable(SingleRefType)) as SingleRefType?;
-                    if (valueDes == null) continue;
+                        specifiedType: const FullType(SingleRefType)) as SingleRefType;
                     result.singleRefType = valueDes;
                     break;
             }
diff --git a/samples/openapi3/client/petstore/python-legacy/petstore_api/models/all_of_with_single_ref.py b/samples/openapi3/client/petstore/python-legacy/petstore_api/models/all_of_with_single_ref.py
index 8466199c80a..e71b49de252 100644
--- a/samples/openapi3/client/petstore/python-legacy/petstore_api/models/all_of_with_single_ref.py
+++ b/samples/openapi3/client/petstore/python-legacy/petstore_api/models/all_of_with_single_ref.py
@@ -57,7 +57,8 @@ class AllOfWithSingleRef(object):
 
         if username is not None:
             self.username = username
-        self.single_ref_type = single_ref_type
+        if single_ref_type is not None:
+            self.single_ref_type = single_ref_type
 
     @property
     def username(self):
diff --git a/samples/server/petstore/php-laravel/lib/app/Models/AllOfWithSingleRef.php b/samples/server/petstore/php-laravel/lib/app/Models/AllOfWithSingleRef.php
index 24ce4ab5c83..90a2bca8d56 100644
--- a/samples/server/petstore/php-laravel/lib/app/Models/AllOfWithSingleRef.php
+++ b/samples/server/petstore/php-laravel/lib/app/Models/AllOfWithSingleRef.php
@@ -12,7 +12,7 @@ class AllOfWithSingleRef {
     /** @var string $username */
     public $username = "";
 
-    /** @var SingleRefType|null $singleRefType */
-    public $singleRefType = null;
+    /** @var SingleRefType $singleRefType */
+    public $singleRefType;
 
 }