message: Skip post processing when no mergeable is found
  Summary: Skip the additional logic if unnecessary.
diff: @@ -639,7 +639,9 @@ std::vector<DexClass*> ModelMerger::merge_model(
  // Write out mapping files
  auto method_dedup_map = mm.get_method_dedup_map();
  write_out_type_mapping(mergeable_to_merger, method_dedup_map, s_mapping_file);
  + if (!to_materialize.empty()) {
  post_process(model, type_tags, mergeable_to_merger_ctor);
  + }
  TRACE(TERA, 3, "created %d merger classes\n", merger_classes.size());
  m_stats.m_num_generated_classes = merger_classes.size();
  