code: @Override
      public Set<JobKey> getJobKeys(final GroupMatcher<JobKey> matcher) throws JobPersistenceException {
          return doWithLock(new LockCallback<Set<JobKey>>() {
              @Override
              public Set<JobKey> doWithLock(JedisCommands jedis) throws JobPersistenceException {
                  return storage.getJobKeys(matcher, jedis);
              }
          }, "Could not retrieve JobKeys.");
      }
docs: Get the keys of all of the <code>{@link org.quartz.Job}</code> s that
  have the given group name.
  <p/>
  <p>
  If there are no jobs in the given group name, the result should be
  an empty collection (not <code>null</code>).
  </p>
  
  @param matcher the matcher for job key comparison