Fix: no-deprecated-api crash on undeclared assignment (fixes #55)

[not-an-aardvark]

When assigning to a standard library module, no-deprecated-api stores the name of the variable that was assigned, and track references to it. However, if the variable has no declaration, it was throwing an error (see #55):

foo = require('fs');

This fixes the issue by adding a null check to ensure that the variable has a declaration.

[codecov-io]

Current coverage is 98.79% (diff: 100%)

Merging #56 into master will increase coverage by 0.22%

@@             master        #56   diff @@
==========================================
  Files            36         36          
  Lines           910        912     +2   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits            897        901     +4   
+ Misses           13         11     -2   
  Partials          0          0          

Powered by Codecov. Last update 382886e...a51a7ff

[mysticatea]

Thank you for the issue & PR!

I'm not sure why I had not been aware of the bug a long time. 😅