Filter Leads by Last Name only

Hello

I've modified the SugarObject Template for Person to not include a first_name field since we only require the last_name field, but now the search for this module is broken

I get the following error whenever I try to search for something 

I've already tried modifying the default filter by creating a custom/Extension/modules/Leads/Ext/clients/base/filters/default/default.php with the following 

but it didn't work

Does anybody know how to modify the default filter to not include the first_name?