code: private void addPolymorphicClusterIds(final OClassImpl iBaseClass) {
      boolean found;
      for (int i : iBaseClass.polymorphicClusterIds) {
        found = false;
        for (int k : polymorphicClusterIds) {
          if (i == k) {
            found = true;
            break;
          }
        }
  
        if (!found) {
          // ADD IT
          polymorphicClusterIds = OArrays.copyOf(polymorphicClusterIds, polymorphicClusterIds.length + 1);
          polymorphicClusterIds[polymorphicClusterIds.length - 1] = i;
          Arrays.sort(polymorphicClusterIds);
        }
      }
    }
docs: Add different cluster id to the "polymorphic cluster ids" array.