code: public boolean hasIdentity(String category, String type) {
          String key = XmppStringUtils.generateKey(category, type);
          return identitiesSet.contains(key);
      }
docs: Returns true if this DiscoverInfo contains at least one Identity of the given category and type.
  
  @param category the category to look for.
  @param type the type to look for.
  @return true if this DiscoverInfo contains a Identity of the given category and type.