[Java] add JSONTest fro RequiredNullableBody class

Author: fanqiewanzi

samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/JSONTest.java

@@ -671,4 +671,13 @@ public void testOneOfAnyOfArray() throws Exception {
             assertTrue(exception.getMessage().contains("java.io.IOException: The JSON string is invalid for"));
         }
     }
+
+    @Test
+    public void testRequiredNullableBody() throws Exception {
+        final String json1 = "{\"integer_prop\":null,\"number_prop\":null,\"boolean_prop\":null,\"string_prop\":null,\"date_prop\":null,\"datetime_prop\":null,\"array_nullable_prop\":null,\"array_and_items_nullable_prop\":null,\"array_items_nullable\":[],\"object_nullable_prop\":null,\"object_and_items_nullable_prop\":null,\"object_items_nullable\":{},\"custom_ref_enum\":null,\"custom_enum\":null}";
+        final RequiredNullableBody body = new RequiredNullableBody();
+
+        assertEquals("{\"array_items_nullable\":[],\"object_items_nullable\":{}}", json.serialize(body));
+        assertEquals(json.deserialize(json1, RequiredNullableBody.class), body);
+    }
 }