public static Expression nullIf(Expression expression1, Expression expression2) {
        return x("NULLIF(" + expression1.toString() + ", " + expression2.toString() + ")");
    }
public static Expression nullIf ( Expression expression1 , Expression expression2 ) { return x ( "NULLIF(" + expression1 . toString ( ) + ", " + expression2 . toString ( ) + ")" ) ; }
Returned expression results in NULL if expression1 = expression2, otherwise returns expression1.
Returns MISSING or NULL if either input is MISSING or NULL..