[Java] fix nullable arrays when JsonNullable is used

[borsch]

Fix for #9996

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cc @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @nmuesch (2021/01)

[wing328]

Tested locally and the result is good.

[mariusmanastireanu]

@borsch / @wing328 - can you please give a short look over #13385 and advice? Thank you