code: @Override
      public String marshal(EUI64 val) throws Exception {
          return val == null ? null : val.toString();
      }
docs: Converts the given {@link EUI64} value to its string representation. Returns {@code null } if
  {@code val} is {@code null}.
  
  @param val The EUI-64 value.
  @return The string representation of {@code val}.
  @see EUI64#toString()