added null test

tests/LuDocParserTest.php

      * @min 42
      * @max 42
      * @between 0 42
-     * @another 1 2 42.42 true false "a string" \'string\'
+     * @another 1 2 42.42 true false "a string" \'string\' null
      * and another
      * @return AnotherType
      */');
                     ["Method" => "min", "Arguments" => [42]],
                     ["Method" => "max", "Arguments" => [42]],
                     ["Method" => "between", "Arguments" => [0, 42]],
-                    ["Method" => "another", "Arguments" => [1, 2, 42.42, true, false, "a string", "string"]]
+                    ["Method" => "another", "Arguments" => [1, 2, 42.42, true, false, "a string", "string", null]]
                 ]
             ]
         ];