Unexpected validation behaviour with empty strings in data

[kshade]

I've found some unexpected (to me) behaviour in WTForms-JSON where an empty string in an optional string field with a minimum length did not result in a validation error nor exclusion of the field from patch_data. I've written a small test script, here is the output I'm getting from it:

WTForms-JSON version 0.3.3

json {}
errors {}
form.data {'name': None, 'potato': None}
form.patch_data {}

json {'name': ''}
errors {}
form.data {'name': None, 'potato': None}
form.patch_data {'name': None}

json {'name': 'a'}
errors {'name': ['Field must be between 2 and 128 characters long.']}
form.data {'name': 'a', 'potato': None}
form.patch_data {'name': 'a'}

json {'name': 'ab'}
errors {}
form.data {'name': 'ab', 'potato': None}
form.patch_data {'name': 'ab'}

json {'potato': None}
errors {}
form.data {'name': None, 'potato': None}
form.patch_data {'potato': None}

json {'potato': ''}
errors {}
form.data {'name': None, 'potato': None}
form.patch_data {'potato': None}

json {'potato': 'minimum'}
errors {'potato': ['Invalid value, must be one of: maximum.']}
form.data {'name': None, 'potato': 'minimum'}
form.patch_data {'potato': 'minimum'}

json {'potato': 'maximum'}
errors {}
form.data {'name': None, 'potato': 'maximum'}
form.patch_data {'potato': 'maximum'}

Length validation doesn't happen with the second test case, but it also isn't removed from patch_data like in the first. Potato intuitively should only ever be "maximum" or not present, but both an empty string and None are accepted as None.

[kshade]

I've tried to debug the problem, it looks like the validation chain is stopped because the Optional validator treats the empty string as the field not being present, but patch_data() still tries to read the field's data value which is set to None.

[kshade]

Hello?