Makes the feature_name field for UserCallout nullable

Changelog: changed

app/graphql/types/user_callout_type.rb

@@ -4,7 +4,7 @@ module Types
   class UserCalloutType < BaseObject # rubocop:disable Graphql/AuthorizeTypes
     graphql_name 'UserCallout'
 
-    field :feature_name, UserCalloutFeatureNameEnum, null: false,
+    field :feature_name, UserCalloutFeatureNameEnum, null: true,
       description: 'Name of the feature that the callout is for.'
     field :dismissed_at, Types::TimeType, null: true,
       description: 'Date when the callout was dismissed.'

doc/api/graphql/reference/index.md

@@ -13383,7 +13383,7 @@ Represents a recorded measurement (object count) for the Admins.
 | Name | Type | Description |
 | ---- | ---- | ----------- |
 | <a id="usercalloutdismissedat"></a>`dismissedAt` | [`Time`](#time) | Date when the callout was dismissed. |
-| <a id="usercalloutfeaturename"></a>`featureName` | [`UserCalloutFeatureNameEnum!`](#usercalloutfeaturenameenum) | Name of the feature that the callout is for. |
+| <a id="usercalloutfeaturename"></a>`featureName` | [`UserCalloutFeatureNameEnum`](#usercalloutfeaturenameenum) | Name of the feature that the callout is for. |
 
 ### `UserCore`