Description:
------------
The documentation on get_class() does not specify what happens when the parameter is omitted. I assumed the parameter defaults to $this, but this is not the case.

Note that this may also be a bug in the implementation instead of the documentation.

Reproduce code:
---------------
<?php
class A {
  function a() {
    echo get_class();
    echo get_class($this);
  }
}

class B extends A { }
$b = new B();
$b->a();
?>

Actual result:
--------------
get_class() in A will return A, where get_class($this) will return B.