Method get_string_optional

uno/options/Options.cpp:200–209

   }

   std::optional<std::string> Options::get_string_optional(const std::string& option_name) const {
      try {
         const std::string& option_value = this->string_options.at(option_name);
         this->used[option_name] = true;
         return option_value;
      }
      catch(const std::out_of_range&) {
         return std::nullopt;
      }
   }

   OptionType Options::get_option_type(const std::string& option_name) const {
      try {