=== Circular Reference Protection
# When we try to serialize, it should NOT infinite loop
--- perl
$VAR1 = [
          {
            'a' => 'b',
            'c' => [
                     {},
                     2
                   ]
          },
          []
        ];
$VAR1->[0]{'c'}[0] = $VAR1->[0];
$VAR1->[1] = $VAR1->[0]{'c'};
[ $VAR1 ]

--- error: E_CIRCULAR