fix allow empty enums

[barbieri]

Seems shopify has it and we're failing. It was a "security measure", but not critical one.

Fixes: #156

[coveralls]

Pull Request Test Coverage Report for Build 229

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 227:	0.0%
Covered Lines:	1481
Relevant Lines:	1481

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💛 - Coveralls