avoid useless JSON roundtrip

know your library they said...

lib/api/v3/work_packages/work_packages_api.rb

@@ -55,17 +55,17 @@ module API
                   # After Pass 1 the correct type information is merged into the WP
                   # In Pass 2 the representer is created with the new type info and will be able
                   # to also parse custom fields successfully
-                  merge_json_into_work_package!(request_body.to_json)
-                  merge_json_into_work_package!(request_body.to_json)
+                  merge_hash_into_work_package!(request_body)
+                  merge_hash_into_work_package!(request_body)
                 end
               end
 
               # merges the given JSON representation into @work_package
-              def merge_json_into_work_package!(json)
+              def merge_hash_into_work_package!(hash)
                 payload = Form::WorkPackagePayloadRepresenter.create(
                   @work_package,
                   enforce_lock_version_validation: true)
-                payload.from_json(json)
+                payload.from_hash(hash)
               end
 
               def request_body