support nullable check for OAS 3.1 (#15698)

samples/openapi3/client/petstore/java/jersey2-java8/api/openapi.yaml

@@ -1973,8 +1973,8 @@ components:
           type: string
     fruitReq:
       additionalProperties: false
+      nullable: true
       oneOf:
-      - type: "null"
       - $ref: '#/components/schemas/appleReq'
       - $ref: '#/components/schemas/bananaReq'
     appleReq:
@@ -2023,8 +2023,8 @@ components:
         in OAS schema >= 3.1.
       discriminator:
         propertyName: shapeType
+      nullable: true
       oneOf:
-      - type: "null"
       - $ref: '#/components/schemas/Triangle'
       - $ref: '#/components/schemas/Quadrilateral'
     NullableShape:

samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/model/Drawing.java

@@ -55,7 +55,7 @@ public class Drawing {
   private Shape mainShape;
 
   public static final String JSON_PROPERTY_SHAPE_OR_NULL = "shapeOrNull";
-  private ShapeOrNull shapeOrNull;
+  private JsonNullable<ShapeOrNull> shapeOrNull = JsonNullable.<ShapeOrNull>undefined();
 
   public static final String JSON_PROPERTY_NULLABLE_SHAPE = "nullableShape";
   private JsonNullable<NullableShape> nullableShape = JsonNullable.<NullableShape>undefined();
@@ -92,7 +92,7 @@ public class Drawing {
 
 
   public Drawing shapeOrNull(ShapeOrNull shapeOrNull) {
-    this.shapeOrNull = shapeOrNull;
+    this.shapeOrNull = JsonNullable.<ShapeOrNull>of(shapeOrNull);
     return this;
   }
 
@@ -101,20 +101,28 @@ public class Drawing {
    * @return shapeOrNull
   **/
   @javax.annotation.Nullable
-  @JsonProperty(JSON_PROPERTY_SHAPE_OR_NULL)
-  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  @JsonIgnore
 
   public ShapeOrNull getShapeOrNull() {
-    return shapeOrNull;
+        return shapeOrNull.orElse(null);
   }
 
-
   @JsonProperty(JSON_PROPERTY_SHAPE_OR_NULL)
   @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
-  public void setShapeOrNull(ShapeOrNull shapeOrNull) {
+
+  public JsonNullable<ShapeOrNull> getShapeOrNull_JsonNullable() {
+    return shapeOrNull;
+  }
+  
+  @JsonProperty(JSON_PROPERTY_SHAPE_OR_NULL)
+  public void setShapeOrNull_JsonNullable(JsonNullable<ShapeOrNull> shapeOrNull) {
     this.shapeOrNull = shapeOrNull;
   }
 
+  public void setShapeOrNull(ShapeOrNull shapeOrNull) {
+    this.shapeOrNull = JsonNullable.<ShapeOrNull>of(shapeOrNull);
+  }
+
 
   public Drawing nullableShape(NullableShape nullableShape) {
     this.nullableShape = JsonNullable.<NullableShape>of(nullableShape);
@@ -232,7 +240,7 @@ public class Drawing {
     }
     Drawing drawing = (Drawing) o;
     return Objects.equals(this.mainShape, drawing.mainShape) &&
-        Objects.equals(this.shapeOrNull, drawing.shapeOrNull) &&
+        equalsNullable(this.shapeOrNull, drawing.shapeOrNull) &&
         equalsNullable(this.nullableShape, drawing.nullableShape) &&
         Objects.equals(this.shapes, drawing.shapes)&&
         Objects.equals(this.additionalProperties, drawing.additionalProperties);
@@ -244,7 +252,7 @@ public class Drawing {
 
   @Override
   public int hashCode() {
-    return Objects.hash(mainShape, shapeOrNull, hashCodeNullable(nullableShape), shapes, additionalProperties);
+    return Objects.hash(mainShape, hashCodeNullable(shapeOrNull), hashCodeNullable(nullableShape), shapes, additionalProperties);
   }
 
   private static <T> int hashCodeNullable(JsonNullable<T> a) {