ValidationErrors initialize check args[:errors] is present

[wuxiaoyi]

ValidationErrors will throw NoMethodError (undefined method `each' for nil:NilClass) when I manually throw a ValidationErrors exception without params.
This argument appears to be necessary, so it should detect the presence or absence of this key. Or give it a default value.
And the fail word should let us know which key is missing.

[dblock]

Thanks!

The first change broke a legit spec. I think it already says "Params are missing", so it's confusing to say "Params are missing: params", no?

The second one looks legit, but in which context do you get it? At least needs a test.

[wuxiaoyi]

@dblock , thank you for your review :-)
I added test and fixes description.

[dblock]

Re-reading all this I have more questions, sorry :)

First, for this implementation. The error should be an ArgumentError. We should also standardize the message matching the rest of Ruby implementations in the core library, so ArgumentError: missing args: errors. If you can please make those changes and squash commits.

Finally, maybe it just makes sense to treat args without errors as an empty array? I am not sure.