Description:
------------
Empty() function throws E_NOTICE "Notice: Undefined index" when checking a class constant of type ARRAY for non-existent element. However, isset() works as expected.

Test script:
---------------
class Test
{
  private $obj;
  const MAP = ['testKey' => 'test'];
  
  function __construct()
  {
    $this->obj       = new \stdClass();
    $this->obj->test = "testObject";
  }

  public function isKey($name = 'testKey') {
    var_dump(empty($this->obj->{static::MAP[$name]}));
    var_dump(empty($this->obj->$name));
  }
}

Expected result:
----------------
Expect to see var_dump() return boolean result of empty() WITHOUT E_NOTICE generation.

Actual result:
--------------
var_dump() correctly returns result of empty(), but also generates E_NOTICE "Notice: Undefined index"