The error associated with the field.
The callback that returns the new array of errors that includes the given error, or returns
the original errors array if there are no changes. By default, if an error is an object that has the message field,
it is added only the message value is distinct; otherwise, if an error isn't an object or doesn't have the
message field, it is added only if it has a unique identity.
Enhances fields with error management methods.