fix(tiptap): don't fail on node without content

app/services/tiptap_service.rb

@@ -44,6 +44,8 @@ class TiptapService
         else
           tags[id]
         end
+      in { type: type } if ["paragraph", "title", "heading"].include?(type) && !node.key?(:content)
+        # noop
       end
     end
 

spec/services/tiptap_service_spec.rb

@@ -21,6 +21,9 @@ RSpec.describe TiptapService do
             type: 'title',
             content: [{ type: 'text', text: 'Title' }]
           },
+          {
+            type: 'title' # remained empty in editor
+          },
           {
             type: 'paragraph',
             attrs: { textAlign: 'right' },
@@ -31,6 +34,10 @@ RSpec.describe TiptapService do
               }
             ]
           },
+          {
+            type: 'paragraph'
+            # no content, empty line
+          },
           {
             type: 'paragraph',
             content: [
@@ -70,6 +77,10 @@ RSpec.describe TiptapService do
             attrs: { level: 3 },
             content: [{ type: 'text', text: 'Heading 3' }]
           },
+          {
+            type: 'heading',
+            attrs: { level: 3 } # remained empty in editor
+          },
           {
             type: 'bulletList',
             content: [