Add method dedup map lookup safety check
Add method dedup map lookup safety check

Reviewed By: justinjhendrick

Differential Revision: D15751465

fbshipit-source-id: 9bc3aa1d983a8b11360d141e832617ddbff57741

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex