only in patch2:
unchanged:
--- a/core/modules/views/src/Plugin/views/display/PathPluginBase.php
+++ b/core/modules/views/src/Plugin/views/display/PathPluginBase.php
@@ -151,16 +151,10 @@ protected function getRoute($view_id, $display_id) {
     // routes (defined via {}). As a name for the parameter use arg_$key, so
     // it can be pulled in the views controller from the request.
     foreach ($bits as $pos => $bit) {
-      if ($bit == '%') {
-        // Generate the name of the parameter using the key of the argument
-        // handler.
-        $arg_id = 'arg_' . $arg_counter++;
-        $bits[$pos] = '{' . $arg_id . '}';
-        $argument_map[$arg_id] = $arg_id;
-      }
-      elseif (strpos($bit, '%') === 0) {
-        // Use the name defined in the path.
-        $parameter_name = substr($bit, 1);
+      if (strpos($bit, '%') === 0) {
+        // Use the name defined in the path. If no name is given then default to
+        // the base entity type for this view.
+        $parameter_name = $bit !== '%' ? substr($bit, 1) : $this->view->getBaseEntityType()->id();
         $arg_id = 'arg_' . $arg_counter++;
         $argument_map[$arg_id] = $parameter_name;
         $bits[$pos] = '{' . $parameter_name . '}';