diff --git a/app/serializers/activity_serializer.rb b/app/serializers/activity_serializer.rb
index 9892fd70d..a5f9fc02d 100644
--- a/app/serializers/activity_serializer.rb
+++ b/app/serializers/activity_serializer.rb
@@ -14,6 +14,8 @@ class ActivitySerializer
   end
 
   attribute "prov:wasAttributedTo" do |object|
+    return nil if object.username.blank?
+    
     url = Rails.env.production? ? "https://api.datacite.org" : "https://api.test.datacite.org"
     object.username.include?(".") ? url + "/clients/" + object.username : url + "/providers/" + object.username
   end
diff --git a/db/schema.rb b/db/schema.rb
index b0b06523a..bc2bdaf4c 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -330,4 +330,4 @@
   add_foreign_key "dataset", "datacentre", column: "datacentre", name: "FK5605B47847B5F5FF"
   add_foreign_key "media", "dataset", column: "dataset", name: "FK62F6FE44D3D6B1B"
   add_foreign_key "metadata", "dataset", column: "dataset", name: "FKE52D7B2F4D3D6B1B"
-end
+end
\ No newline at end of file