” = empty string and/or NULL…
How many times have you seen
'' used for a NULL string?
Oracle 9i SQL Reference Release 2 (9.2) – “Basic Elements of Oracle SQL, 5 of 10: Nulls”
“…Oracle currently treats a character value with a length of zero as null. However, this may not continue to be true in future releases, and Oracle recommends that you do not treat empty strings the same as nulls.”