Issue #2978668: FormStateInterface missing

bootstrap_barrio.theme

@@ -8,6 +8,7 @@
 use Drupal\Core\Template\Attribute;
 use Drupal\Core\Link;
 use Drupal\Component\Utility\Html;
+use Drupal\Core\Form\FormStateInterface;
 
 /**
  * Implements hook_preprocess_HOOK() for HTML document templates.

composer.json

+{
+    "name": "drupal/bootstrap_barrio",
+    "description": "Bootstrap 4 base theme. Flex based and compatible with jQuery 3+.",
+    "type": "drupal-theme",
+    "license": "GPL-2.0",
+    "homepage": "https://www.drupal.org/project/bootstrap_barrio",
+    "authors": [{
+        "name": "Alberto Siles",
+        "email": "alberto@siles.pe"
+    }],
+}
\ No newline at end of file