Merge pull request #11 from visuellverstehen/10-fix-undefined-text-property

fix: prevent call to undefined text property

Author: juliawarnke

src/Nodes/Heading.php

@@ -18,7 +18,10 @@ public function renderHTML($node, $HTMLAttributes = [])
 
         // Add slugified id to specific headlines.
         if (in_array($node->attrs->level, config('anchor-navigation.heading.levels', []))) {
-            $HTMLAttributes['id'] = Str::slug($node->content[0]->text);
+
+            if (property_exists($node->content[0], 'text') && !is_null($node->content[0]->text)) {
+                $HTMLAttributes['id'] = Str::slug($node->content[0]->text);
+            }
         }
 
         return [