handle NumberFormatException by throwing a ValidationException

without this malformed numbers (in our case "nan" coming from collectd python plugin) would result in a large stacktrace in the log file, with this exception wrapping it handles it quite nicely. I also think that ValidationException is fair to throw, although arguably one could add a Validator that makes sure all fields that are supposed to be numbers are in fact numbers.
let me know if you prefer this.