The BizTalk Mapper creates a blank attribute in an element of the output document when there is a link created from an optional field in the source schema to a destination field. This occur even if the incoming document does not contain that optional attribute.
For example, if you have an incoming document where the optional BCT05 attribute of the BCT element is not present and the BCT05 attribute is linked to the destination attribute BCT05, the following would occur:
BCT05 in the destination document specification is optional. By using the "Incorrect Result" output, if the BCT05 attribute has min/max length that is set to greater than 0, the output document fails to validate against the destination document specification, because the BCT05 attribute incorrectly exists with a length of 0.