Dedupe fails on address field in 5.12
Something introduced in 5.12 adds this line, but the right hand side should be a string not an array. https://github.com/civicrm/civicrm-core/blob/master/CRM/Dedupe/BAO/Rule.php#L110
https://civicrm.stackexchange.com/questions/29210/merge-dedupe-using-organisation-rules-db-error
I can make a PR.