When using an "is not" filter operator, the query does not return results where the field is empty or null. Also the operators "is different from" or "same as" exclude null values from comparisons.
Steps to Reproduce
This is expected behaviour for modern databases such as MySQL, SQL Server, and Oracle. The way the "not equal to" operator is behaving in the SN platform is congruent with standards-compliant SQL dialect.
Additional information on the SQL operator can be found in the stackoverflow article Not equal <> != operator on NULL
Related Problem: PRB659408