Fix crash when exporting with destructuring and sparse array

[jfmengels]

Hi there!

The tests for eslint-plugin-import are currently failing, with the Cannot read property 'type' of null error.

I tracked down the error to Babylon and the new checks to whether a duplicate export exists, and have fixed it in this PR.

I have created a minimal viable example, which is available in my first commit, to show that the tests fail unexpectedly with the error message above. It looks like this

export const { foo: [ ,, qux7 ] } = bar;

(Actually, export const [,, a] = {} would have sufficed, but I just noticed it, and have already updated the expected.json file in the tests, which took me a while 😅... let me know if you prefer I use this form instead, or add both cases in the tests)

The problem is that the code here loops through the elements inside the destructuring expression, but forgets to filter out the null ones, that you get when you have a sparse array like [,,a], before directly accessing the type property.

I added a null check around the recursive call, and that fixes the problem.

Let me know if you need more info, more work or anything else :)

[hzoo]

Nope that looks good/makes sense! Thanks a lot!!

[hzoo]

and have already updated the expected.json file in the tests, which took me a while

@jfmengels If you create an actual.js without an expected it should automatically make the file - hopefully you didn't mean you did it manually 😅 , but if so next time!

Will merge + release after travis is done

[jfmengels]

hopefully you didn't mean you did it manually 😅 , but if so next time!

Haha, I did... 😅

I didn't know how tests were created, so I just updated an existing test, which already had the file. Deleting it was not the most intuitive thing to do 😄.

Honestly I just thought you were working like a madman to have proper expected.json files. This makes much more sense 😄. (Though, if you don't write it at least in part manually, I'm not sure what exacly you're testing, but that's another topic). I myself cheated a bit by using astexplorer.net, and then manually fixing every error the tests showed me. I will definitely remember it next time.

Will merge + release after travis is done

Awesome! Thanks for being so reactive!