In route

             # Defines a routes where id is optional parameter
            Route::get('/users/{id?}', 'UserController@get');

            # Defines a routes where id is required parameter
            Route::get('/users/{id}', 'UserController@get');

            

in controller

in optional case

            public function get( $id = null)
            {
                if (!$id) {
                    // get id
                }
              
            }


            

in mandatory case

            public function get( $id)
            {
               //get id
              
            }


            

validate route parameters

            # Define a route where id should be numeric only
            Route::get('/users/{id}', 'UserController@get')->where('id', '[0-9]+');

            # Define a route where name should be alpha only
            Route::get('/users/{name}', 'UserController@get')->where('name', '[A-Za-z]+');

            # Define a route where name should be alpha only and id should be numeric only
            Route::get('/users/{id}/{name}', 'UserController@get')->where(['id' => '[0-9]+', 'name' => '[a-z]+']);