fix: potential NPE of WriteParameters#hashCode

[bednar]

Closes #482

Proposed Changes

Fixed potential NPE for WriteParameters#hashCode.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• mvn test completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[vlastahajek]

LGTM

[codecov-commenter]

Codecov Report

Base: 88.38% // Head: 88.42% // Increases project coverage by +0.04% 🎉

Coverage data is based on head (36ae228) compared to base (9b07e6e).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #483      +/-   ##
============================================
+ Coverage     88.38%   88.42%   +0.04%     
- Complexity      764      777      +13     
============================================
  Files           172      172              
  Lines          7008     7008              
  Branches        378      380       +2     
============================================
+ Hits           6194     6197       +3     
+ Misses          694      692       -2     
+ Partials        120      119       -1     

Impacted Files	Coverage Δ
...ava/com/influxdb/client/write/WriteParameters.java	83.92% <100.00%> (+3.57%)	⬆️
...a/com/influxdb/client/internal/BucketsApiImpl.java	71.16% <0.00%> (+0.61%)	⬆️

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