code: private synchronized void remove(final String jobIdentifier) {
      final RunningJobImpl result = this.jobs.remove(jobIdentifier);
      if (null == result) {
        throw new RuntimeException("Trying to remove a RunningJob that is unknown: " + jobIdentifier);
      }
    }
docs: A guarded remove() that throws an exception if no RunningJob is known for this id.
  
  @param jobIdentifier