There are two kinds of “null” that are often called out as mistakes, you may be thinking of. One is the null reference, as found in languages like C and Java, which Tony Hoare, who created it for ALGOL back in the sixties, has called his “billion dollar mistake”. The other is the three-valued-logic of null in SQL, which is almost as bad.
There’s nothing wrong with “null”, necessarily, in other contexts, although I do think a more clear name for whatever it means in any given context might be better.