static Map<KnownVersion, Map<MessageType, Command>> makeUnmodifiable(
      final Map<KnownVersion, ConcurrentMap<MessageType, Command>> modifiableMap) {
    final Map<KnownVersion, Map<MessageType, Command>> unmodifiableMap =
        new LinkedHashMap<>(modifiableMap.size());
    for (Map.Entry<KnownVersion, ConcurrentMap<MessageType, Command>> e : modifiableMap
        .entrySet()) {
      unmodifiableMap.put(e.getKey(), unmodifiableMap(e.getValue()));
    }
    return unmodifiableMap(unmodifiableMap);
  }
Iterate through all the Geode versions add a command to the map for that version

@return returns true if command was registered or same command was already registered,
        otherwise false.
@throws InternalGemFireError if a different command was already registered.
geode-core/src/main/java/org/apache/geode/internal/cache/tier/sockets/CommandInitializer.java