mono/mono — pull request #653 by martinpotter (2013-06-03 14:39:36+00:00)
Title: TimeSpan.TryParseExact should not try to parse null input.

TimeSpan.TryParseExact would previously throw a NullReferenceException constructing the Parser when it accesses the Length property of the input string. Microsoft's implementation returns false when null is passed as the input string to parse.