Change >> to a NOT IN instead of IS
Unfortunately this is not going to change any time soon.  I made a decision a while ago that `IS` would be treated as a separate lookup even if it is only ever used with `NULL`.  Similarly, negation is always handled by the unary negation operator and is not special cased.

Since `.where(field << (...)` equates to a `WHERE field IN (...)`, it stands to reason that a `.where(field >> (...)` would equate to `WHERE field NOT IN (...)`.

Then a `.where(field == None)` would equate to `WHERE field IS NULL` and `.where(field != None)` equates to `WHERE field IS NOT NULL`.

Does that not make more sense?
