There's only one call site where we could pass in a null sheet, so let's add a check there and replace the check in addRulesFromSheet() by an assertion.
Created attachment 119737 [details] Patch
Comment on attachment 119737 [details] Patch Clearing flags on attachment: 119737 Committed r103159: <http://trac.webkit.org/changeset/103159>
All reviewed patches have been landed. Closing bug.