Fix: Allowing Empty UserID as valid field

[mnoman09]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 773

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 89.91%

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Files with Coverage Reduction	New Missed Lines	%
core-api/src/main/java/com/optimizely/ab/Optimizely.java	1	93.31%

Totals
Change from base Build 770:	-0.04%
Covered Lines:	2691
Relevant Lines:	2993

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💛 - Coveralls

[thomaszurkan-optimizely]

LGTM. But, I still question whether we should allow empty user ids as valid.

[mnoman09]

@thomaszurkan-optimizely Yes there are testcases of checking empty user id as valid added in fullstack compatibility suite. @mikeng13 can you please elaborate further.

[mikeproeng37]

Yeah we decided at some point to allow empty strings as they are a valid way to use the API. They result in a valid bucketing number and kind of serves as a way to allow binary ON/OFF usage of APIs like isFeatureEnabled where the developer doesn't have to deal with user IDs