[Bugfix][Java] Fixed jersey clients for multiple file upload

[MatteoMolinari93]

Tested locally, haven't opened a Issue since the change required less effort and is small.

@bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @martin-mfg

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[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[wing328]

minor suggestion: add a docstring explaining what this function does

[wing328]

thanks for the PR

I wonder if you've time to fix the same issue in jersey2 ApiClient.java as well: modules/openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache

[MatteoMolinari93]

thanks for the PR

I wonder if you've time to fix the same issue in jersey2 ApiClient.java as well: modules/openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache

Only if this fix comes in the next version ;) done