Entity reference autocomplete's "Add another item" button doesn't work with PostgreSQL

Problem/Motivation

There is a bug in "add another" button inside the entity reference field when using the PostgreSQL database. The bug consists on a sql error inside the ajax requisition, as shown on the attached image, saying that '' isn't a valid integer. This error doesn't happens when using a MySQL database.

Proposed resolution

After some bug tracking, I've found that the root of the problem is that, inside the entityreference_field_widget_form function, there is an entity_load call sending an empty string as an entity_id. The clean solution is if the id is empty inside a previous foreach lace on the code. After this simple change the problem is solved.