Fix Retry strategy example code (#2527)

* Fix ShouldHandle example

* Fix retry-pattern-overusing-builder in snippet source

* retry snippets: fix null-ref warning; IDE0305 suggestion

Author: marcrocny

docs/strategies/retry.md

@@ -474,18 +474,18 @@ Use collections and simple predicate functions:
 
 <!-- snippet: retry-pattern-overusing-builder -->
 ```cs
-ImmutableArray<Type> networkExceptions = new[]
-{
+ImmutableArray<Type> networkExceptions =
+[
     typeof(SocketException),
     typeof(HttpRequestException),
-}.ToImmutableArray();
+];
 
-ImmutableArray<Type> strategyExceptions = new[]
-{
+ImmutableArray<Type> strategyExceptions =
+[
     typeof(TimeoutRejectedException),
     typeof(BrokenCircuitException),
     typeof(RateLimitRejectedException),
-}.ToImmutableArray();
+];
 
 ImmutableArray<Type> retryableExceptions = networkExceptions
     .Union(strategyExceptions)
@@ -494,7 +494,8 @@ ImmutableArray<Type> retryableExceptions = networkExceptions
 var retry = new ResiliencePipelineBuilder()
     .AddRetry(new()
     {
-        ShouldHandle = ex => new ValueTask<bool>(retryableExceptions.Contains(ex.GetType())),
+        ShouldHandle = args
+            => ValueTask.FromResult(args.Outcome.Exception != null && retryableExceptions.Contains(args.Outcome.Exception.GetType())),
         MaxRetryAttempts = 3,
     })
     .Build();

src/Snippets/Docs/Retry.cs

@@ -174,18 +174,18 @@ public static void Pattern_OverusingBuilder()
     {
         #region retry-pattern-overusing-builder
 
-        ImmutableArray<Type> networkExceptions = new[]
-        {
+        ImmutableArray<Type> networkExceptions =
+        [
             typeof(SocketException),
             typeof(HttpRequestException),
-        }.ToImmutableArray();
+        ];
 
-        ImmutableArray<Type> strategyExceptions = new[]
-        {
+        ImmutableArray<Type> strategyExceptions =
+        [
             typeof(TimeoutRejectedException),
             typeof(BrokenCircuitException),
             typeof(RateLimitRejectedException),
-        }.ToImmutableArray();
+        ];
 
         ImmutableArray<Type> retryableExceptions = networkExceptions
             .Union(strategyExceptions)
@@ -194,7 +194,9 @@ public static void Pattern_OverusingBuilder()
         var retry = new ResiliencePipelineBuilder()
             .AddRetry(new()
             {
-                ShouldHandle = ex => new ValueTask<bool>(retryableExceptions.Contains(ex.GetType())),
+                ShouldHandle = args
+                    => ValueTask.FromResult(args.Outcome.Exception is not null
+                        && retryableExceptions.Contains(args.Outcome.Exception.GetType())),
                 MaxRetryAttempts = 3,
             })
             .Build();