def __call__(self, value):
if isinstance(value, str):
value = IFromUnicode(self.field).fromUnicode(value)
# Mimic what z3c.form does in it's BaseDataConverter.
if isinstance(value, str):
value = value.strip()
if value == "":
value = self.field.missing_value
self.field.validate(value)
return value
