conditional split error

hi

i m getting this error:

[Conditional Split 1 [14]] Error: The expression "[Expiration Date] != [Expiration Date_LookUp] || BAC == "X" || ISNULL(BAC)" on "Conditional Split 1.Outputs[Case 1]" evaluated to NULL, but the "Conditional Split 1" requires a Boolean results. Modify the error row disposition on the output to treat this result as False (Ignore Failure) or to redirect this row to the error output (Redirect Row).  The expression results must be Boolean for a Conditional Split.  A NULL expression result is an error.

how to solve it