code: private Severity calculateSeverity(ILoggingEvent event) {
          if (event.getLevel().equals(Level.ERROR)) {
              return Severity.ERROR;
          } else if (event.getLevel().equals(Level.WARN)) {
              return Severity.WARNING;
          }
          return Severity.INFO;
      }
docs: Calculates the severity based on the logging event
  @param event the event
  @return The Bugsnag severity