Edit forms does not work in PHP 7.3

Problem/Motivation

When I used entityconnect on a Drupal 7 with PHP 7.3, I cannot used the entityconnect edit form.
It returns a gray screen with an error 500 send by headers.

Proposed resolution

The problems comes from PHP 7.3 wich do not allow multiple implicite conversion after a variable initialization.

In the function entityconnect_add_edit_button_submit the variable $target_id is initialized as text but can be used as an array.

Changing initialization solved the problem.

From : $target_id = '';
To : $target_id = NULL;