Make rotation nullable

doc/api/graphql/reference/index.md

@@ -3333,7 +3333,7 @@ Describes an incident management on-call schedule.
 | `description` | [`String`](#string) | Description of the on-call schedule. |
 | `iid` | [`ID!`](#id) | Internal ID of the on-call schedule. |
 | `name` | [`String!`](#string) | Name of the on-call schedule. |
-| `rotation` | [`IncidentManagementOncallRotation!`](#incidentmanagementoncallrotation) | On-call rotation for the on-call schedule. |
+| `rotation` | [`IncidentManagementOncallRotation`](#incidentmanagementoncallrotation) | On-call rotation for the on-call schedule. |
 | `rotations` | [`IncidentManagementOncallRotationConnection!`](#incidentmanagementoncallrotationconnection) | On-call rotations for the on-call schedule. |
 | `timezone` | [`String!`](#string) | Time zone of the on-call schedule. |
 

ee/app/graphql/types/incident_management/oncall_schedule_type.rb

@@ -35,7 +35,7 @@ module Types
 
       field :rotation,
             OncallRotationType,
-            null: false,
+            null: true,
             description: 'On-call rotation for the on-call schedule.',
             resolver: ::Resolvers::IncidentManagement::OncallRotationsResolver.single
     end