code: @Override
      public EUI48 unmarshal(String str) throws Exception {
          return str == null ? null : EUI48.fromString(str);
      }
docs: Converts the EUI-48 string representation in {@code str} to an {@link EUI48}. Returns
  {@code null} if {@code str} is {@code null}.
  
  @param str The EUI-48 string representation.
  @return The {@link EUI48} represented by {@code str}.
  @throws IllegalArgumentException if {@code str} is not a valid EUI-48 string representation.
  @see EUI48#fromString(String)