CRM-19431 The empty array that it's not really empty

Thanks for filing this and working on a fix. Can you please submit your change to the master branch first and then we can look at backporting it to LTS?

I ran into the same issue. A 4.6.21 site was throwing a fatal error on Basic Search form, "Cannot recognize 0 for 2". I tracked this down to CRM/Contact/BAO/ContactType.php basicTypeInfo() passing CRM_Core_DAO::$_nullArray to CRM_Core_DAO::executeQuery, where CRM_Core_DAO::$_nullArray is not empty but has 23 elements, which appear to be tag id => tag name for a subset of the tags.
Haven't been able to replicate on demo. The backtrace involves Views, in my case.

Created PR https://github.com/civicrm/civicrm-core/pull/9376 . This is similar to Ruben's patch here, the differences being...
1. I found Ruben's patch gave a strict warning "Only variables should be passed by reference", due to using ''$nullArray = array()" as an argument in a function call.
2. I decided on a belt-and-braces approach, fixing both the pollution (in EntityTag) and use (in ContactType) of CRM_Core_DAO::$_nullArray.

Thanks, Coleman Watts for merging the PR against master. Would be good to get the fix in 4.6, shall I create another PR against 4.6?

Yes please.

PR for 4.6: https://github.com/civicrm/civicrm-core/pull/9391