code: @Override
      public Set<TriggerKey> getTriggerKeys(final GroupMatcher<TriggerKey> matcher) throws JobPersistenceException {
          return doWithLock(new LockCallback<Set<TriggerKey>>() {
              @Override
              public Set<TriggerKey> doWithLock(JedisCommands jedis) throws JobPersistenceException {
                  return storage.getTriggerKeys(matcher, jedis);
              }
          }, "Could not retrieve TriggerKeys.");
      }
docs: Get the names of all of the <code>{@link org.quartz.Trigger}</code> s
  that have the given group name.
  <p/>
  <p>
  If there are no triggers in the given group name, the result should be a
  zero-length array (not <code>null</code>).
  </p>
  
  @param matcher the matcher with which to compare trigger groups