[java] Allow null input in FluentWait

[valfirst]

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Description

input in FluentWait should be handled by users in Function<? super T, V> isTrue.

Motivation and Context

There is no reason to require input if Function implementation doesn't require such input. More generic solution is to overload the methods to allow to pass Supplier alongside with Function, but it will require changes in API.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7b41033) 58.48% compared to head (2bd1602) 58.48%.
Report is 4 commits behind head on trunk.

❗ Current head 2bd1602 differs from pull request most recent head af69b34. Consider uploading reports for the commit af69b34 to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##            trunk   #13558   +/-   ##
=======================================
  Coverage   58.48%   58.48%           
=======================================
  Files          86       86           
  Lines        5270     5270           
  Branches      220      220           
=======================================
  Hits         3082     3082           
  Misses       1968     1968           
  Partials      220      220           

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