fix: handle optional nullable fields without default values

Author: jorgerod

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaDefaultValueRenderer.java

@@ -1,20 +1,3 @@
-/*
- * Copyright 2018 OpenAPI-Generator Contributors (https://openapi-generator.tech)
- * Copyright 2018 SmartBear Software
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
 package org.openapitools.codegen.languages;
 
 import com.fasterxml.jackson.databind.JsonNode;