PHP & MySQL username submit problem

Question

I want to allow users to either have there username field empty at any time but I get the username error message Your username is unavailable! how can I correct thi

Answer 1

if(isset($_POST['username']) && trim($_POST['username'])!=='') {

Otherwise, $_POST['username'] will be set even if the form is submitted with an empty field.

Answer 2

if(isset($_POST['username']) && !empty($_POST['username'])) {
...