protected void readIndex(
     ObjectContainerBase stream, ClassMetadata clazz, ByteArrayBuffer reader) {
   int indexID = reader.readInt();
   if (!stream.maintainsIndices() || !(stream instanceof LocalObjectContainer)) {
     return;
   }
   if (btree(clazz) != null) {
     return;
   }
   clazz.index().read(stream, validIndexId(indexID));
   if (isOldClassIndex(indexID)) {
     new ClassIndexesToBTrees_5_5().convert((LocalObjectContainer) stream, indexID, btree(clazz));
     stream.setDirtyInSystemTransaction(clazz);
   }
 }