title: Exception for missing data
body: <p>I was wondering what kind of exception should one throw for missing data. For example if an xml node doesn't contain data. It would be easy to "<strong>throw new Exception(...)</strong>" but this is not recommended. Another option would be to create a new exception class like <strong>MissingDataException</strong> or <strong>InvalidDataException</strong> but isn't there a built-in exception class for this case?</p>