[java][model] Collection initialized to empty collection even if not required

[jmini]

We are trying to use the same model between our client (using a model serialized with Jackson) and server (JaxRS jersey2).

If a collection is not required, the server model set its value to null.

openapi-generator/modules/openapi-generator/src/main/resources/JavaJaxRS/pojo.mustache

Lines 24 to 29 in 7f36f26

	{{#isContainer}}
	private {{{datatypeWithEnum}}} {{name}}{{#required}} = {{{defaultValue}}}{{/required}}{{^required}} = null{{/required}};
	{{/isContainer}}
	{{^isContainer}}
	private {{{datatypeWithEnum}}} {{name}}{{#defaultValue}} = {{{.}}}{{/defaultValue}};
	{{/isContainer}}

This is not the case on client side.

openapi-generator/modules/openapi-generator/src/main/resources/Java/pojo.mustache

Line 61 in 7f36f26

private {{{datatypeWithEnum}}} {{name}}{{#defaultValue}} = {{{.}}}{{/defaultValue}};

In my opinion this should be aligned.

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[bkabrda]

👍 from my side. It also leads to problems like always sending empty {} when you don't touch a value of that attribute, which can be problematic when doing PATCH requests that are only expected to change certain parts of the resource, but with this issue they actually reset some attributes to empty.

[viclovsky]

I use rest-assured client for testing.
The issue leads to inability to check that a field is definitely absent (by comparing by null), because collections are always empty.

[jmini]

@bkabrda thank you for your feedback, you wrote exactly what I wanted to add. This is a valid argument for people who are interested only in the java-client (and do not care about client and server being aligned).

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I have proposed the change in PR #3615