#21 enum does not accept empty value

[Evert Mouw]

When using an enum, the yml file did not validate is the field was empty, even when the field was not required.

As a workaround, I have used a regexp. Luckily, by default the field contains a space, to I could tell the pattern to accept that as well.

#enum: [fixed, click, variable]
pattern: /fixed|click|variable|[ ]/

Best is of course to have an enum that, if the field is not required, also accepts "no value".