Fix errors when blocks don't have collapse settings.

Author: rupertj

src/Plugin/Block/CollapsibleTrait.php

@@ -16,7 +16,6 @@ public function blockForm($form, FormStateInterface $form_state) {
       '#title' => $this->t('Collapsible'),
       '#description' => $this->t('<insert description>'),
       '#default_value' => $this->configuration['collapsible'] ?? 0,
-
     ];
 
     $form['collapse_width'] = [
@@ -42,12 +41,23 @@ public function blockSubmit($form, FormStateInterface $form_state): void {
     $this->configuration['collapse_width'] = $form_state->getValue('collapse_width');
   }
 
+  /**
+   * Add collapsible data to a block build.
+   */
   protected function addCollabsibleData(array &$output) {
+
+    $collapsible = (bool) $this->configuration['collapsible'] ?? FALSE;
+    $collapseWidth = (int) $this->configuration['collapse_width'] ?? 0;
+
+    // This needs a width to work.
+    if ($collapseWidth === 0) {
+      $collapsible = FALSE;
+    }
+
     $output['#attached']['drupalSettings']['localgov_publications'][$this->pluginId] = [
-      'collapsible' => (bool) $this->configuration['collapsible'],
-      'collapse_width' => (int) $this->configuration['collapse_width'],
+      'collapsible' => $collapsible,
+      'collapse_width' => $collapseWidth,
     ];
-
     $output['#attached']['library'][] = 'localgov_publications/localgov-publications-blocks';
   }