Anyone who has used Sheet Set Manager has most likely wanted/needed to make a field blank. The time I run into this the most is with the fields I have for our revision dates. Obviously, with a first submission I am not going to have a "Revised Date"; thus the need for a blank field.
Unfortunately simply entering a space doesn't cut it for Sheet Set Manager (SSM). There are two secrets (that I know about) to blank out these fields.
The first and perhaps the simplest is to simply enter "U+00A0" into your field. Another way is to press the "Alt" key and at the same time press "0160".