Find Pledges search returns error on dmaster
Reproduce: https://dmaster.demo.civicrm.org/civicrm/pledge/search?reset=1 click "Search" with or without filters.
Result: Error: Call to a member function getSearchFieldMetadata() on null in CRM_Core_Form_Search::formRule() (line 181 of /srv/buildkit/build/dmaster/sites/all/modules/civicrm/CRM/Core/Form/Search.php).
Confirmed on local install of 5.12 as well.