Node ID contextual filter uses wrong handler

+1 for the fix, of course!

Added test coverage (not just for the issue described but for the whole nid argument handler)

+++ b/core/modules/views/src/Plugin/views/PluginBase.php
@@ -396,7 +396,7 @@ function ($children, $elements) {
-      return (string) $this->getRenderer()->render($build);
+      return (string) $this->getRenderer()->renderPlain($build);

I had to borrow this line from #2492839: Views replacement token bc layer allows for Twig template injection via arguments to make my test pass.

+++ b/core/modules/node/src/Tests/Views/NidArgumentTest.php
@@ -0,0 +1,114 @@
+    $view = View::create([
+      'id' => $view_id,
+      'base_table' => 'node_field_data',
+      'display' => [
+        'default' => [
+          'display_plugin' => 'page',
+          'id' => 'default',
+          'display_options' => [
+            'path' => 'test/%',
+            'fields' => [
+              'nid' => [
+                'table' => 'node_field_data',
+                'field' => 'nid',
+                'id' => 'nid',
+                'plugin_id' => 'field',
+              ],
+            ],
+            'arguments' => [
+              'nid' => [
+                'table' => 'node_field_data',
+                'field' => 'nid',
+                'id' => 'nid',
+                'plugin_id' => 'numeric',
+                'title_enable' => TRUE,
+                'title' => '%1',
+              ],
+            ],
+          ],
+        ],
+      ],
+    ]);

IMHO we should use a file, if possible.

Yeah, I guess it does make more sense to use a real views export there.
Also fixed the test since we shouldn't be using the %1 syntax anymore but rather {{ arguments.nid }}

Yeah! As always I like if things are actually broken and we can expand our test coverage.

This is bug with a non-disruptive fix - permitted in beta. Committed 7f11ec7 and pushed to 8.0.x. Thanks!