Description:
------------
I am using the charter position for doing something with string and for some reason when a string is empty it will automatic cast to array which i am not sure is it supposed to happen.

Test script:
---------------
$str = "";
$str[0] = "b";
var_dump($str);

$str = "a";
$str[0] = "b";
var_dump($str);

Expected result:
----------------
string(1) "b"
string(1) "b"

Actual result:
--------------
array(1) {
  [0]=>
  string(1) "b"
}
string(1) "b"