Add null check

[philipnilsson]

I'm encountering an error in babel.dev.js/exit. It's in quite a large project, and I don't have time to figure out the reason. (It fails checking a dependency called js-csp). Hoping you'll consider adding this extra check.

[codecov-io]

Codecov Report

Merging #861 into next will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             next     #861   +/-   ##
=======================================
  Coverage   86.97%   86.97%           
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  Files          30       30           
  Lines         622      622           
  Branches      147      147           
=======================================
  Hits          541      541           
  Misses         65       65           
  Partials       16       16

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[theKashey]

The change looks reasonable, and I am going to merge your PR.
The only thing I am asking for - could you change your plugin code to

 exit({ node }, {file}) {
          const registrations = node[REGISTRATIONS]
          if(!registrations) {
              console.error('no program enter', file);
          }

next double check the content of that file, and roughly explain (or copy paste code here) how you created a program you can leave, but do not enter.

I can see the reason to this in the current implementation, it might be some serious bug, hiding between lines.