Description:
------------
i use anonymous function in other function when there is array union operator (+) above of this anonymous then the variable convert to NULL .

Test script:
---------------
class foo {
  public function test($o = array()){
    $o += array('test');
    $func = function(){};
    var_dump($func);
  }
}
$foo = new foo;
$foo->test();

Expected result:
----------------
object(Closure)#2 (1) {
  ["this"]=>
  object(x)#1 (0) {
  }
}

Actual result:
--------------
NULL