An empty field in a Sheet Set will display dashes (—-). You want to display nothing, just a blank field. To avoid displaying —- enter a character from the font Character Map that represents a space.

The method for entering characters:

• Hold down the Alt key.
• On the number pad type the 4 numbers that represent the character in the character map.

To enter a Null Value (space character) for blank fields in a sheet set use ALT+0160