Fix unpermitted params error in VSA

This change fixes the unpermitted params error when the incoming params
are manipulated in the service.

ee/app/services/analytics/cycle_analytics/value_streams/create_service.rb

@@ -9,7 +9,7 @@ module Analytics
         def initialize(group:, params:, current_user:, value_stream: ::Analytics::CycleAnalytics::GroupValueStream.new(group: group))
           @value_stream = value_stream
           @group = group
-          @params = process_params(params.dup)
+          @params = process_params(params.dup.to_h)
           @current_user = current_user
         end
 
@@ -34,10 +34,8 @@ module Analytics
         attr_reader :value_stream, :group, :params, :current_user
 
         def process_params(raw_params)
-          if raw_params[:stages]
-            raw_params[:stages_attributes] = raw_params.delete(:stages)
-            raw_params[:stages_attributes].map! { |attrs| build_stage_attributes(attrs) }
-          end
+          raw_params[:stages_attributes] = raw_params.delete(:stages) || []
+          raw_params[:stages_attributes].map! { |attrs| build_stage_attributes(attrs) }
 
           raw_params
         end

ee/spec/controllers/groups/analytics/cycle_analytics/value_streams_controller_spec.rb

@@ -135,6 +135,17 @@ RSpec.describe Groups::Analytics::CycleAnalytics::ValueStreamsController do
           expect(json_response['id']).to eq(value_stream.id)
           expect(json_response['stages'].first['title']).to eq('updated stage name')
         end
+
+        context 'when deleting the stage by excluding it from the stages array' do
+          let(:value_stream_params) { { name: 'no stages', stages: [] } }
+
+          it 'returns a successful 200 response' do
+            put :update, params: { id: value_stream.id, group_id: group, value_stream: value_stream_params }
+
+            expect(response).to have_gitlab_http_status(:ok)
+            expect(json_response['stages']).to be_empty
+          end
+        end
       end
     end
   end