Remove superfluous isNull checks
Remove superfluous isNull checks

The !isEmpty check already implies !isNull.

Review URL: https://codereview.chromium.org/149873002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@166123 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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