fixed the missing ucd issue

[agy-why]

now the existence of the ucd key is checked (not guarantied).

[coveralls]

Pull Request Test Coverage Report for Build 3827884884

• 2 of 3 (66.67%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 65.888%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
daiquiri/core/generators.py	2	3	66.67%
<!--	Total:	2	3	66.67%	-->

Totals
Change from base Build 3822213246:	0.005%
Covered Lines:	4599
Relevant Lines:	6980

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💛 - Coveralls

[kimakan]

I see what you mean. Due to the fact that the metadata in the QueryJob model is a JSON field, the presence of the ucd field is not guaranteed. This makes sense since the users are allowed to upload their own tables where the ucd field is not required. Interestingly, the existence of the fields arraysize and datatype is checked before accessing it, unlike the ucd field. I'm closing the PR with this. :-)

[agy-why]

The reason why ucd was not checked, was because we introduced it later, while implementing the datalink protocol. And forgot that there is no guaranty that ucd is there. So it was really a BUG.