Fix profile plugin value bug

src/Form/HmDisplayProfileForm.php

@@ -79,7 +79,7 @@ class HmDisplayProfileForm extends EntityForm {
         '#type' => 'radios',
         '#title' => $this->t('Display plugin'),
         '#options' => $display_plugin_labels,
-        '#default_value' => $hm_display_profile->get("plugin") ?: ['hm_display_jstree'],
+        '#default_value' => $hm_display_profile->get("plugin") ?: 'hm_display_jstree',
         '#description' => $this->t('Display plugin that is in charge of rendering the hierarchy view.'),
         '#required' => TRUE,
       ];