Replace some Map.containsKey with patterns

[natebosch]

In a few expressions where we check for the presence of a key, and then immediately read that key, refactor to an if-case which decomposes the variable inline.

[coveralls]

Pull Request Test Coverage Report for Build 10293217659

Details

• 3 of 3 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 84.53%

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Totals
Change from base Build 10015285761:	-0.03%
Covered Lines:	1295
Relevant Lines:	1532

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💛 - Coveralls

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.53%. Comparing base (62562fe) to head (4c57a1f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #490 +/- ## ========================================== - Coverage 84.56% 84.53% -0.04% ========================================== Files 35 35 Lines 1535 1532 -3 ========================================== - Hits 1298 1295 -3 Misses 237 237 ```

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