code: public Job schedule(Runnable runnable, Schedule when) {
  		return schedule(null, runnable, when);
  	}
docs: Schedule the executions of a process.
  
  @param runnable The process to be executed at a schedule
  @param when The {@link Schedule} at which the process will be executed
  @return The corresponding {@link Job} created.
  @throws NullPointerException if {@code runnable} or {@code when} are {@code null}
  @throws IllegalArgumentException if the same instance of {@code runnable} is
  scheduled twice whereas the corresponding job status is not {@link JobStatus#DONE}