check non-nullness of required parameters

[tangiel]

@nAmed parameters that don't have @nullable parameters are deemed
required. Endpoints v2 lost this request validation, but this change
adds it back in. Previously, the framework would assume the validation
was done.

[codecov-io]

Codecov Report

Merging #148 into master will increase coverage by 0.06%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             master     #148      +/-   ##
============================================
+ Coverage     80.01%   80.08%   +0.06%     
- Complexity     1678     1726      +48     
============================================
  Files           156      156              
  Lines          5595     5694      +99     
  Branches        730      766      +36     
============================================
+ Hits           4477     4560      +83     
- Misses          840      844       +4     
- Partials        278      290      +12

Impacted Files	Coverage Δ	Complexity Δ
.../server/spi/request/ServletRequestParamReader.java	83.59% <66.66%> (-0.41%)	28 <2> (+4)
...rver/spi/config/validation/ApiConfigValidator.java	79.33% <0%> (+2.76%)	109% <0%> (+44%)	⬆️

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[kryzthov]

Looks good, just one nitpick question.

[kryzthov]

Any reason to turn the else if/else into a nested else { if/else }?
It looks strictly equivalent, am I misreading?

[tangiel]

It was just so that the null check can exist in the newly created else block, rather than re-checking for parameter name existence. Everything else is equivalent.