A new string modifier has been added to the Synchronizer mapping screens which will help to identify empty strings:
Using the Boolean logic of the IsEmpty modifier, coupled with a Conditional Modifier String and a Constant modifier, you can inject default data into field values. This removes the need for convoluted workarounds in either the original source or by a complex combination of other modifiers.
NOTE: modifiers cannot be used on the matching key field, currently those values must be valid in the source data.
The field modifier also supports an option that allows the modifier to ignore any whitespace characters it may encounter in the input (like non-breaking spaces, tabs, and other special characters). Thus a string that wholly comprises of those whitespace characters would be treated as empty.
These changes are made available in Build 85