fix: add null validation for java enum arguments

[optionsome]

Description

This fixes an issue with generated java query input arguments as enum values lacked null checks.

Related #637

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Screenshots/Sandbox (if appropriate/relevant):

https://stackblitz.com/edit/github-val3pw

How Has This Been Tested?

Updated unit tests and tested locally that this fixes a problem in a project that I'm using this dependency for.

Checklist:

• I have followed the
  CONTRIBUTING doc and the
  style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[changeset-bot]

🦋 Changeset detected

Latest commit: ea505fb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@graphql-codegen/java	Patch

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[saihaj]

Thank you!

[saihaj]

released @graphql-codegen/java@4.0.1