[Java] better default value handling (#14130)

* add test for array default value

* update null return

* minor fixes

* move default value tests to echo api spec

* add new files

* remove unused files

* fix enum array default, add tests

* better array init

* Update modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java

Co-authored-by: Leonard Brünings <lord_damokles@gmx.net>

* Update modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java

Co-authored-by: Leonard Brünings <lord_damokles@gmx.net>

* revert the fix

* improve default value handling

* update native samples, add tests

* update samples

* fix tests

* use conditional test for timezone

* add tests to apache http client echo api

* add option to default container to null

* fix map default value

* minor refactoring

* update samples

* fix javadoc

* fix pom.xml

* add tests in java native echo client

* add java apache client echo tests

* fix test

* fix test

---------

Co-authored-by: Leonard Brünings <lord_damokles@gmx.net>

samples/client/echo_api/java/apache-httpclient/docs/DefaultValue.md

@@ -0,0 +1,29 @@
+
+
+# DefaultValue
+
+to test the default value of properties
+
+## Properties
+
+| Name | Type | Description | Notes |
+|------------ | ------------- | ------------- | -------------|
+|**arrayStringEnumDefault** | [**List<ArrayStringEnumDefaultEnum>**](#List<ArrayStringEnumDefaultEnum>) |  |  [optional] |
+|**arrayStringDefault** | **List<String>** |  |  [optional] |
+|**arrayIntegerDefault** | **List<Integer>** |  |  [optional] |
+|**arrayString** | **List<String>** |  |  [optional] |
+|**arrayStringNullable** | **List<String>** |  |  [optional] |
+|**stringNullable** | **String** |  |  [optional] |
+
+
+
+## Enum: List<ArrayStringEnumDefaultEnum>
+
+| Name | Value |
+|---- | -----|
+| SUCCESS | "success" |
+| FAILURE | "failure" |
+| UNCLASSIFIED | "unclassified" |
+
+
+