code: @Nullable
    public static Long tryParseLong(@Nullable String string)
    {
      return Strings.isNullOrEmpty(string)
             ? null
             : Longs.tryParse(string.charAt(0) == '+' ? string.substring(1) : string);
    }
docs: To fix semantic difference of Longs.tryParse() from Long.parseLong (Longs.tryParse() returns null for '+' started value)