Fix error when default VS is requested

This change fixes the error when the initial, in-memory default
value stream is requested.

ee/app/controllers/groups/analytics/cycle_analytics_controller.rb

@@ -33,6 +33,12 @@ class Groups::Analytics::CycleAnalyticsController < Groups::Analytics::Applicati
   def load_value_stream
     return unless @group && params[:value_stream_id]
 
-    @value_stream = @group.value_streams.find(params[:value_stream_id])
+    default_name = Analytics::CycleAnalytics::Stages::BaseService::DEFAULT_VALUE_STREAM_NAME
+
+    @value_stream = if params[:value_stream_id] == default_name
+                      @group.value_streams.new(name: default_name)
+                    else
+                      @group.value_streams.find(params[:value_stream_id])
+                    end
   end
 end

ee/changelogs/unreleased/324673-fix-error-on-default-vsa-page.yml

+---
+title: Fix 500 error when refreshing Value Stream Analytics page with a default stage
+merge_request: 56761
+author:
+type: fixed

ee/spec/controllers/groups/analytics/cycle_analytics_controller_spec.rb

@@ -35,6 +35,27 @@ RSpec.describe Groups::Analytics::CycleAnalyticsController do
 
       expect(response).to render_template :show
     end
+
+    context 'when the initial, default value stream is requested' do
+      let(:value_stream_id) { Analytics::CycleAnalytics::Stages::BaseService::DEFAULT_VALUE_STREAM_NAME }
+
+      before do
+        get(:show, params: { group_id: group, value_stream_id: value_stream_id })
+      end
+
+      it 'renders the default in memory value stream' do
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(assigns[:value_stream].name).to eq(value_stream_id)
+      end
+
+      context 'when invalid name is given' do
+        let(:value_stream_id) { 'not_default' }
+
+        it 'renders 404 error' do
+          expect(response).to have_gitlab_http_status(:not_found)
+        end
+      end
+    end
   end
 
   context 'when the license is missing' do