[6.x] Use concrete assertions, not exists (#23271)#23392

Merged

stacey-gammon merged 1 commit intoelastic:6.xfrom stacey-gammon:backport/6.x/pr-23271

Sep 24, 2018

+18-22

Commits on Sep 21, 2018

Use concrete assertions, not exists (elastic#23271 )
stacey-gammon
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