fix the Undefined type and background

avatars_gravatar/src/Plugin/AvatarGenerator/GravatarGenerator.php

@@ -58,8 +58,9 @@ class GravatarGenerator extends AvatarGeneratorBase {
         'wavatar' => $this->t('Wavatar'),
         'retro' => $this->t('8-bit style avatar'),
       ],
-      '#default_value' => $this->configuration['type'],
+      '#default_value' => isset($this->configuration['type']) ? $this->configuration['type'] : 'identicon', // Provide a default value here.
     ];
+       
     return $form;
   }