fix

app/models/project_category.rb

@@ -20,4 +20,7 @@ class ProjectCategory < ApplicationRecord
   include Projectable
   has_ancestry
 
+  def logo_url
+    ""
+  end
 end

app/views/project_categories/pinned_index.json.jbuilder

@@ -1 +1 @@
-json.project_categories @project_categories, :id, :name
+json.project_categories @project_categories, :id, :name, :logo_url