Return a "Not found" error instead of "Invalid review"

src/api/app/models/bs_request.rb

@@ -736,6 +736,8 @@ def create_new_review(opts)
     )
     return newreview if newreview.valid?
 
+    newreview.check_reviewer!
+
     raise InvalidReview, 'Review invalid: ' + newreview.errors.full_messages.join("\n")
   end
 

src/api/app/models/review.rb

@@ -302,6 +302,11 @@ def staging_project?
     for_project? && !project&.staging_workflow_id.nil?
   end
 
+  def check_reviewer!
+    selected_errors = errors.select { |error| error.attribute.in?([:user, :group, :project, :package]) }
+    raise ::NotFoundError, selected_errors.map { |error| "#{error.attribute.capitalize} not found" }.to_sentence if selected_errors.any?
+  end
+
   private
 
   def matches_maintainers?(user)

src/api/spec/models/bs_request_spec.rb

@@ -1,8 +1,5 @@
 require 'rails_helper'
-# WARNING: If you change tests make sure you uncomment this line
-# and start a test backend. Some of the BsRequestAction methods
-# require real backend answers for projects/packages.
-# CONFIG['global_write_through'] = true
+
 RSpec.describe BsRequest, vcr: true do
   let(:user) { create(:confirmed_user, :with_home, login: 'tux') }
   let(:target_project) { create(:project, name: 'target_project') }
@@ -122,10 +119,10 @@
     it { expect(request.state).to eq(:review) }
     it { expect(request.commenter).to eq(reviewer.login) }
 
-    it 'fails with reasonable error' do
+    it 'fails with not found' do
       expect { request.addreview(by_user: 'NOEXIST') }.to raise_error do |exception|
-        expect(exception).to be_a(BsRequest::InvalidReview)
-        expect(exception.message.to_s).to eq("Review invalid: User can't be blank")
+        expect(exception).to be_a(NotFoundError)
+        expect(exception.message).to eq('User not found')
       end
     end
   end