ASA Database Administration Guide
  Database Options
    Alphabetical list of options

TDS_EMPTY_STRING_IS_NULL option [database]

Function 

Controls whether empty strings are returned as NULL or a string containing one blank character for TDS connections.

Allowed values 

ON, OFF

Default 

OFF

Description 

By default, this option is set to OFF and empty strings are returned as a string containing one blank character for TDS connections. When this option is set to ON, empty strings are returned as NULL strings for TDS connections. Non-TDS connections distinguish empty strings from NULL strings.