docs: protected void checkJobType(final String jobName, final Class<?> jobType) {
          if (jobName == null) {
              throw new IllegalArgumentException("jobName must not be null");
          }
          if (jobType == null) {
              throw new IllegalArgumentException("jobType must not be null");
          }
          if (!(Runnable.class.isAssignableFrom(jobType)) 
                  && !(Callable.class.isAssignableFrom(jobType))) {
              throw new IllegalArgumentException(
                      "jobType must implement either Runnable or Callable: " + jobType);
          }
      }