Add ArrayExpression.elements.default

[jmm]

I'd like to add a test for this, but #3174 isn't merged yet :(

[codecov-io]

Current coverage is 85.02%

Merging #3261 into master will decrease coverage by -0.24% as of 0f85e79

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  Files          215     215       
  Stmts        15706   15706       
  Branches      3360    3360       
  Methods          0       0       
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- Hit          13391   13354    -37
- Partial        673     709    +36
- Missed        1642    1643     +1

Review entire Coverage Diff as of 0f85e79

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[amasad]

why is the test dependent on #3174?

[jmm]

@amasad babel-types has no test infrastructure currently. I suppose I could test it indirectly via some other package, but to me it seems better to get tests up and running for babel-types.

[amasad]

ah, cool. In what cases does ArrayExpression need a default?

[hzoo]

I suppose if you want to do t.arrayExpression() instead of t.arrayExpression([])

[jmm]

@amasad Yes, just what @hzoo said: when you have reason to insert an empty array literal into the AST.