code: private Throwable extractThrowable(ILoggingEvent event) {
          IThrowableProxy throwableProxy = event.getThrowableProxy();
          if (throwableProxy instanceof ThrowableProxy) {
              return ((ThrowableProxy) throwableProxy).getThrowable();
          }
  
          return null;
      }
docs: Gets the throwable from the log event (if any)
  @param event The log event
  @return The throwable (or null)