code: public static String[] getMissingSipMethods(Collection<String> sipMethods) {
          String[] methods = {};
          if (sipMethods.size() > 0 && sipMethods.containsAll(ALL_SIP_METHODS) == false) {
              HashSet<String> missingMethods = new HashSet<String>(ALL_SIP_METHODS);
              missingMethods.removeAll(sipMethods);
              methods = new String[missingMethods.size()];
              missingMethods.toArray(methods);
          }
          return methods;
      }
docs: Get sip methods in ALL_SIP_METHODS not in the argument sipMethods.
  
  @param sipMethods a set of sip method names
  @return possibly empty sip methods in ALL_SIP_METHODS not in sipMethods.