May be in a situation where you are creating a new mysqli object.
$MyConnection = new mysqli($hn, $un, $pw, $db);
but even after you close the object
$MyConnection->close();
if you will use print_r() to check the contents of $MyConnection, you will get an error as below:
Error:
mysqli Object
Warning: print_r(): Property access is not allowed yet in /path/to/program on line ..
( [affected_rows] => [client_info] => [client_version] =>.................)
in which case you can't use unlink() because unlink() will require a path name string but in this case $MyConnection is an Object.
So you have another choice of setting its value to null:
$MyConnection = null;
now things go right, as you have expected. You don't have any content inside the variable $MyConnection as well as you already cleaned up the mysqli Object.
It's a recommended practice to close the Object before setting the value of your variable to null.