message: das.cli: use a shorter argument placeholder
diff: @@ -261,8 +261,8 @@ namespace elle
  static inline std::string const&
  nothing()
  {
  - // Quite unlikely with ten \0 characters, but ok in the logs.
  - static auto const res = std::string("NOTHING") + std::string(10, 0);
  + // A marker, quite unlikely to be an effective argument.
  + static auto const res = '{' + std::string(1, 0) + '}';
  return res;
  }
  