private Object readResolve() throws ObjectStreamException {
    return fromOrdinal(ordinal); // Canonicalize
  }
converts allowed values in cache.xml into ExpirationAction

@param xmlValue the values allowed are: invalidate, destroy, local-invalidate, local-destroy
@return the corresponding ExpirationAction
@throws IllegalArgumentException for all other invalid strings.
geode-core/src/main/java/org/apache/geode/cache/ExpirationAction.java