Fix approvals.

Rx.NET/Source/src/System.Reactive/Threading/Tasks/TaskObservableExtensions.cs

@@ -552,7 +552,7 @@ namespace System.Reactive.Threading.Tasks
         /// <param name="scheduler">The scheduler used for overriding where the task completion signals will be issued.</param>
         /// <returns>A task that will receive the last element or the exception produced by the observable sequence.</returns>
         /// <exception cref="ArgumentNullException"><paramref name="observable"/> or <paramref name="scheduler"/> is <c>null</c>.</exception>
-        public static Task<TResult> ToTask<TResult>(this IObservable<TResult> observable, CancellationToken cancellationToken, object state, IScheduler scheduler)
+        public static Task<TResult> ToTask<TResult>(this IObservable<TResult> observable, CancellationToken cancellationToken, object? state, IScheduler scheduler)
         {
             return observable.ToTask(cancellationToken, state).ContinueOnScheduler(scheduler);
         }

Rx.NET/Source/tests/Tests.System.Reactive.ApiApprovals/Api/ApiApprovalTests.Core.verified.cs

@@ -2527,13 +2527,13 @@ namespace System.Reactive.Threading.Tasks
         public static System.IObservable<TResult> ToObservable<TResult>(this System.Threading.Tasks.Task<TResult> task) { }
         public static System.IObservable<TResult> ToObservable<TResult>(this System.Threading.Tasks.Task<TResult> task, System.Reactive.Concurrency.IScheduler scheduler) { }
         public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable) { }
-        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, object state) { }
         public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, System.Reactive.Concurrency.IScheduler scheduler) { }
         public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, System.Threading.CancellationToken cancellationToken) { }
-        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, object state, System.Reactive.Concurrency.IScheduler scheduler) { }
-        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, System.Threading.CancellationToken cancellationToken, object state) { }
+        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, object? state) { }
         public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, System.Threading.CancellationToken cancellationToken, System.Reactive.Concurrency.IScheduler scheduler) { }
-        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, System.Threading.CancellationToken cancellationToken, object state, System.Reactive.Concurrency.IScheduler scheduler) { }
+        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, System.Threading.CancellationToken cancellationToken, object? state) { }
+        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, object? state, System.Reactive.Concurrency.IScheduler scheduler) { }
+        public static System.Threading.Tasks.Task<TResult> ToTask<TResult>(this System.IObservable<TResult> observable, System.Threading.CancellationToken cancellationToken, object? state, System.Reactive.Concurrency.IScheduler scheduler) { }
     }
 }
 namespace System.Runtime.CompilerServices