code: public RiakFlag getFlag(BinaryValue key)
      {
          if (entries.containsKey(key))
          {
              for (RiakDatatype dt : entries.get(key))
              {
                  if (dt.isFlag())
                  {
                      return dt.getAsFlag();
                  }
              }
          }
          return null;
      }
docs: Returns a RiakFlag to which the specified key is mapped, or {@literal null}
  if no RiakFlag is present.
  
  @param key key whose associated RiakFlag is to be returned.
  @return a RiakFlag, or null if one is not present.