Prevent NPE in findTypeFromGenericInArguments

[TimvdLippe]

There was only a single test failing on this. I think the issue was RETURNS_SMART_NULLS in combination with an ArgumentCaptor, but
couldn't figure that part out. At least this fixes prevented the NPE.

[raphw]

I cannot really forsee the consequences of this but it does not seem like a problem, especially since a null pointer is never a good outcome. Can we support this with a test case?

[codecov-io]

Codecov Report

Merging #1648 into release/2.x will increase coverage by <.01%.
The diff coverage is 100%.

@@                Coverage Diff                @@
##             release/2.x    #1648      +/-   ##
=================================================
+ Coverage          87.37%   87.38%   +<.01%     
- Complexity          2434     2435       +1     
=================================================
  Files                301      301              
  Lines               6275     6278       +3     
  Branches             783      784       +1     
=================================================
+ Hits                5483     5486       +3     
  Misses               596      596              
  Partials             196      196

Impacted Files	Coverage Δ	Complexity Δ
...aultanswers/RetrieveGenericsForDefaultAnswers.java	96.15% <100%> (+0.23%)	21 <0> (+1)	⬆️

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[mockitoguy]

Nice change, thank you!