"Does not contain" excludes NULL values

When I use a 'Does not contain' option in a grouped filter, fields where the value is NULL do not match the filter. This is because in mySQL, "NOT LIKE" on a NULL value returns NULL, not TRUE.

I've patched the views string handler to accommodate for this by including an "OR IS NULL" on the op_not operator function.

This may have been handled elsewhere - it seems obvious - and there may be a better way of handling it, but my search found nothing. My apologies if I've duplicated an issue.