the get_option_group definition was missing from the splitting of the calls.

Author: phlptp

include/CLI/impl/App_inl.hpp

@@ -433,6 +433,15 @@ CLI11_NODISCARD CLI11_INLINE CLI::App_p App::get_subcommand_ptr(int index) const
     throw OptionNotFound(std::to_string(index));
 }
 
+CLI11_NODISCARD CLI11_INLINE CLI::App *App::get_option_group(std::string group_name) const {
+for(const App_p &app : subcommands_) {
+    if(app->name_.empty() && app->group_ == group_name) {
+        return app.get();
+    }
+}
+throw OptionNotFound(group_name);
+    }
+
 CLI11_NODISCARD CLI11_INLINE std::size_t App::count_all() const {
     std::size_t cnt{0};
     for(const auto &opt : options_) {