[Java] add nullable annotation to pojo template for non-required fields

[kassim]

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Description of the PR

fixes #3264

adds @javax.annotation.Nullable to non-required fields, to enhance IDE feedback and Kotlin-interop

this requires the com.google.code.findbugs:jsr305:3.0.2 dependency for the annotation - I'm not sure where I should adjust the sample dependencies (I adjusted the pom.xml / build.gradle in the sample but the integration test still fails) documentation to inform people this

existing tests are working fine, I don't think additional ones are necessary

[wing328]

@kassim thanks for the PR. Can you use the following instead to avoid blank lines or trailing spaces?

  {{^required}}
  @javax.annotation.Nullable
  {{/required}}

[wing328]

I'll do it in another PR.

[wing328]

Filed #3453

[wing328]

@kassim thanks for the PR, which has been included in the 4.1.0 release: https://twitter.com/oas_generator/status/1160000504455319553

[kassim]

cheers 🍺 glad to have contributed to the project

[szczebel]

Is there a way to switch this off when using openapi-generator-maven-plugin?
In case I don't want jsr305 on classpath, I would like to have an option such as:

<configOptions>
  <generate.javax.annotation.Nullable>false</generate.javax.annotation.Nullable>
</configOptions>