Don't fail on empty services metadata
Don't fail on empty services metadata

Summary: It is possible to get empty metadata just now - specifically if someone overrides the AsyncProcessor and does not implement the getServiceMetadata the default implementation returns nothing.

Reviewed By: sethdelliott, praihan

Differential Revision: D30644254

fbshipit-source-id: 23c056d319eaa020c2cfbbe6cfaaa4fae48ff1a6

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