In MappedAttributeImpl#updateRecord, if the string value is blank, set the default instead (or null if there is no default). MappedElementImpl#isEmpty will then determine that a record is empty when it would otherwise just have a blank attribute. The result is that elements with blank values are not present in the MODS. References #117.
Add "Omitted When Blank" attribute to the MappedAttribute class (default is true). Check this when setting blank values to blank in updateRecord. (References #117)
don't set a blank default value if we're omitting blank attributes