Map<Object, Object> sourceMap = new LinkedHashMap<>();
        for (Entry<?, ?> entry : entries) {
          if (sourceMap.put(entry.getKey(), entry.getValue()) != null) {
            throw new UnsupportedOperationException("duplicate key");
          }
        }
        return ImmutableBiMap.copyOf(sourceMap);
      }
    },
    COPY_OF_ENTRIES {
      @Override

     *
     * @param sourceMap The source map containing the date field.
     * @param name The name of the date field.
     * @return The Date object, or null if the field doesn't contain a valid date.
     */
    protected Date getDateFromSource(final Map<String, Object> sourceMap, final String name) {
        final Object obj = sourceMap.get(name);
        if (obj instanceof Date) {