Update params to allow setting values to nil

Add specs for missing cases

ee/app/graphql/mutations/incident_management/oncall_rotation/base.rb

@@ -42,7 +42,7 @@ module Mutations
 
           params[:participants] = find_participants(participants)
           params[:starts_at] = parse_datetime(schedule, args[:starts_at]) if args[:starts_at]
-          params[:ends_at] = parse_datetime(schedule, args[:ends_at]) if args[:ends_at]
+          params[:ends_at] = parse_datetime(schedule, args[:ends_at]) if args.key?(:ends_at)
 
           if args[:rotation_length]
             params.merge!(
@@ -51,7 +51,7 @@ module Mutations
             )
           end
 
-          if args[:active_period].present?
+          if args.key?(:active_period)
             active_period_start, active_period_end = active_period_times(args)
             params.merge!(
               active_period_start: active_period_start,

ee/spec/graphql/mutations/incident_management/oncall_rotation/update_spec.rb

@@ -85,6 +85,10 @@ RSpec.describe Mutations::IncidentManagement::OncallRotation::Update do
           context 'when endsAt is nil' do
             let(:ends_at) { nil }
 
+            before do
+              rotation.update!(ends_at: Time.current)
+            end
+
             it 'returns the on-call rotation with no errors' do
               expect(resolve[:oncall_rotation].ends_at).to be_nil
               expect(resolve[:errors]).to be_empty
@@ -165,6 +169,21 @@ RSpec.describe Mutations::IncidentManagement::OncallRotation::Update do
         end
       end
 
+      context 'removing active period' do
+        before do
+          rotation.update!(active_period_start: "08:00", active_period_end: "17:00")
+
+          args.merge!(active_period: nil)
+        end
+
+        it 'removes the active period' do
+          expect(resolve[:errors]).to be_empty
+
+          expect(rotation.reload.active_period_start).to eq(nil)
+          expect(rotation.active_period_end).to eq(nil)
+        end
+      end
+
       describe 'error cases' do
         context 'user cannot be found' do
           before do