1$unset_var = 10;
2unset($unset_var);
3
4$variation_array = array(
5  'unset var' => @$unset_var,
6  'undefined var' => @$undefined_var,
7  'empty string DQ' => "",
8  'empty string SQ' => '',
9  'uppercase NULL' => NULL,
10  'lowercase null' => null,
11  );