RFR: 8305971: NPE in JavacProcessingEnvironment for missing enum constructor body [v4]

[Vicente Romero]

> Please review this simple fix that is averting a NPE in JavacProcessingEnvironment if a an annotation processor is used while compiling this erroneous code:
> 
> 
> enum T {
>   ONE("");
> 
>   T(String one);  // missing constructor body
> 
>   final String one;
> }
> 
> the fix is a one liner
> TIA

Vicente Romero has updated the pull request incrementally with two additional commits since the last revision:

 - missed change in test
 - minor change to test

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15974/files
  - new: https://git.openjdk.org/jdk/pull/15974/files/222287d6..3620f2e6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15974&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15974&range=02-03

  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15974.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15974/head:pull/15974

PR: https://git.openjdk.org/jdk/pull/15974