def try_trigger(event_name)
      if valid_state?(event_name)
        yield
      else
        exception = InvalidStateError
        catch_error(exception) ||
          fail(exception, "inappropriate current state '#{current}'")

        false
      end
    end
def try_trigger(event_name)
      if valid_state?(event_name)
        yield
      else
        exception = InvalidStateError
        catch_error(exception) ||
          fail(exception, "inappropriate current state '#{current}'")

        false
      end
    end
Attempt performing event trigger for valid state

 @return [Boolean]
   true is trigger successful, false otherwise

 @api private