Description:
------------
The 'switch' statement does not correctly handle the case where the switch value === null.


Reproduce code:
---------------
The following code should show "null", "true", "false":

 function testSwitch( $v )
 {
  return $v;
 }

 function showResult( $r )
 {
  $v = testSwitch( $r );

  switch ($v)
  {
   case false:
    echo "false";
    break;
   case null:
    echo "null";
    break;
   case true:
    echo "true";
    break;
  }
   echo "\n<br/>";
 }

 showResult( null );
 showResult( true );
 showResult( false );


Expected result:
----------------
null
true
false


Actual result:
--------------
false
true
false