@Override
  public Set<PdxType> getPdxTypesForClassName(String className) {
    CopyOnWriteHashSet<PdxType> pdxTypeSet = classToType.get(className);
    if (pdxTypeSet == null) {
      return Collections.emptySet();
    } else {
      return pdxTypeSet.getSnapshot();
    }
  }
adds a PdxType for a field to a {@code className => Set<PdxType>} map
geode-core/src/main/java/org/apache/geode/pdx/internal/PeerTypeRegistration.java