Fix usage of javax.annotation (#6645)

* Fix usage of javax.annotation:javax.annotation-api

* Regenerate samples

```
bin/generate-samples.sh bin/configs/java-* bin/configs/jaxrs-* bin/configs/spring-* bin/configs/kotlin-* bin/configs/other/java-* bin/configs/other/jaxrs-* bin/configs/other/kotlin-* bin/configs/other/openapi3/jaxrs-cxf-client.yaml bin/configs/other/openapi3/kotlin-*
```

samples/server/petstore/java-undertow/.openapi-generator/FILES

@@ -0,0 +1,14 @@
+README.md
+pom.xml
+src/main/java/org/openapitools/handler/PathHandlerProvider.java
+src/main/java/org/openapitools/model/Category.java
+src/main/java/org/openapitools/model/ModelApiResponse.java
+src/main/java/org/openapitools/model/Order.java
+src/main/java/org/openapitools/model/Pet.java
+src/main/java/org/openapitools/model/Tag.java
+src/main/java/org/openapitools/model/User.java
+src/main/resources/META-INF/services/com.networknt.server.HandlerProvider
+src/main/resources/config/oauth/primary.crt
+src/main/resources/config/openapi.json
+src/main/resources/config/security.json
+src/main/resources/config/server.json

samples/server/petstore/java-undertow/.openapi-generator/VERSION

@@ -1 +1 @@
-4.0.1-SNAPSHOT
+5.0.0-SNAPSHOT

samples/server/petstore/java-undertow/pom.xml

@@ -16,7 +16,8 @@
         <java.version>1.8</java.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <version.framework>0.1.1</version.framework>
-        <version.jackson>2.8.2</version.jackson>
+        <version.jackson>2.9.10</version.jackson>
+        <version.jackson.databind>2.9.10.4</version.jackson.databind>
         <version.slf4j>1.7.21</version.slf4j>
         <version.jose4j>0.5.2</version.jose4j>
         <version.antlr4>4.5.3</version.antlr4>
@@ -80,7 +81,7 @@
         <dependency>
             <groupId>com.fasterxml.jackson.core</groupId>
             <artifactId>jackson-databind</artifactId>
-            <version>${version.jackson}</version>
+            <version>${version.jackson.databind}</version>
         </dependency>
         <dependency>
             <groupId>com.fasterxml.jackson.core</groupId>
@@ -107,6 +108,12 @@
             <artifactId>swagger-annotations</artifactId>
             <version>${version.swagger}</version>
         </dependency>
+        <!-- @Nullable annotation -->
+        <dependency>
+            <groupId>com.google.code.findbugs</groupId>
+            <artifactId>jsr305</artifactId>
+            <version>3.0.2</version>
+        </dependency>
 
         <!-- Test Dependencies -->
         <dependency>

samples/server/petstore/java-undertow/src/main/java/org/openapitools/model/Pet.java

@@ -22,7 +22,7 @@ import org.openapitools.model.Tag;
 public class Pet   {
   
   private Long id;
-  private Category category = null;
+  private Category category;
   private String name;
   private List<String> photoUrls = new ArrayList<String>();
   private List<Tag> tags = new ArrayList<Tag>();