hide error merging behind contract.validate

lib/api/contracts/model_contract.rb

@@ -55,25 +55,21 @@ module API
       validate :readonly_attributes_unchanged
       validate :run_attribute_validations
 
-      # Performs validation of both, the contract and the underlying model and returns
-      # the merged validation errors for both of them.
-      def validate_contract_and_model
-        self.validate
+      def validate
+        super.validate
         model.valid?
 
-        merged_errors = self.errors.dup
-
         # We need to merge the contract errors with the model errors in
         # order to have them available at one place.
         # This is something we need as long as we have validations split
         # among the model and its contract.
         model.errors.keys.each do |key|
           model.errors[key].each do |message|
-            merged_errors.add(key, message)
+            errors.add(key, message)
           end
         end
 
-        merged_errors
+        errors.empty?
       end
 
       private

lib/api/v3/work_packages/work_packages_api.rb

@@ -70,13 +70,12 @@ module API
                 send_notifications: send_notifications)
 
               contract = UpdateContract.new(@work_package, current_user)
-              errors = contract.validate_contract_and_model
-              if errors.empty? && update_service.save
+              if contract.validate && update_service.save
                 @work_package.reload
 
                 work_package_representer
               else
-                fail ::API::Errors::ErrorBase.create(errors)
+                fail ::API::Errors::ErrorBase.create(contract.errors)
               end
             end