Steps to Reproduce:

• Have more than 100 tasks which you have flagged
• Navigate to https://phabricator.wikimedia.org/flag/
• Given that you have had many flagged tasks, click Next at the bottom.
  • Can be reproduced with an arbitrary ?after=### request parameter.

Actual Results:

• You get the following error:

Call to undefined method PhabricatorFlagQuery::withIDs()

Expected Results:

• The next page shows.