code: public static UnsignedInteger valueOf(String string, int radix) {
      return fromIntBits(UnsignedInts.parseUnsignedInt(string, radix));
    }
docs: Returns an {@code UnsignedInteger} holding the value of the specified {@code String}, parsed as
  an unsigned {@code int} value in the specified radix.
  
  @throws NumberFormatException if the string does not contain a parsable unsigned {@code int}
  value