From 5f4c4773cafff38a85bd8a59cfb66bef0a61b7b5 Mon Sep 17 00:00:00 2001
From: ZLoo <Kozlov.s.v.1992@gmail.com>
Date: Mon, 22 Jul 2024 21:09:11 +0300
Subject: [PATCH] Fix warning CA1062#FallbackPolicy

---
 src/Polly/Fallback/FallbackPolicy.cs          | 12 ++++++---
 .../Fallback/FallbackTResultSpecs.cs          | 27 +++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/src/Polly/Fallback/FallbackPolicy.cs b/src/Polly/Fallback/FallbackPolicy.cs
index 67eed44f058..f45cfc9ddba 100644
--- a/src/Polly/Fallback/FallbackPolicy.cs
+++ b/src/Polly/Fallback/FallbackPolicy.cs
@@ -4,7 +4,6 @@ namespace Polly.Fallback;
 /// <summary>
 /// A fallback policy that can be applied to delegates.
 /// </summary>
-#pragma warning disable CA1062 // Validate arguments of public methods
 public class FallbackPolicy : Policy, IFallbackPolicy
 {
     private readonly Action<Exception, Context> _onFallback;
@@ -69,8 +68,14 @@ internal FallbackPolicy(
 
     /// <inheritdoc/>
     [DebuggerStepThrough]
-    protected override TResult Implementation(Func<Context, CancellationToken, TResult> action, Context context, CancellationToken cancellationToken) =>
-        FallbackEngine.Implementation(
+    protected override TResult Implementation(Func<Context, CancellationToken, TResult> action, Context context, CancellationToken cancellationToken)
+    {
+        if (action is null)
+        {
+            throw new ArgumentNullException(nameof(action));
+        }
+
+        return FallbackEngine.Implementation(
             action,
             context,
             ExceptionPredicates,
@@ -78,4 +83,5 @@ protected override TResult Implementation(Func<Context, CancellationToken, TResu
             _onFallback,
             _fallbackAction,
             cancellationToken);
+    }
 }
diff --git a/test/Polly.Specs/Fallback/FallbackTResultSpecs.cs b/test/Polly.Specs/Fallback/FallbackTResultSpecs.cs
index 62e42e3ec4f..26719da3cea 100644
--- a/test/Polly.Specs/Fallback/FallbackTResultSpecs.cs
+++ b/test/Polly.Specs/Fallback/FallbackTResultSpecs.cs
@@ -6,6 +6,33 @@ public class FallbackTResultSpecs
 {
     #region Configuration guard condition tests
 
+    [Fact]
+    public void Should_throw_when_action_is_null()
+    {
+        var flags = BindingFlags.NonPublic | BindingFlags.Instance;
+        Func<Context, CancellationToken, EmptyStruct> action = null!;
+        PolicyBuilder<EmptyStruct> policyBuilder = new PolicyBuilder<EmptyStruct>(exception => exception);
+        Action<DelegateResult<EmptyStruct>, Context> onFallback = (_, _) => { };
+        Func<DelegateResult<EmptyStruct>, Context, CancellationToken, EmptyStruct> fallbackAction = (_, _, _) => EmptyStruct.Instance;
+
+        var instance = Activator.CreateInstance(
+            typeof(FallbackPolicy<EmptyStruct>),
+            flags,
+            null,
+            [policyBuilder, onFallback, fallbackAction],
+            null)!;
+        var instanceType = instance.GetType();
+        var methods = instanceType.GetMethods(flags);
+        var methodInfo = methods.First(method => method is { Name: "Implementation", ReturnType.Name: "EmptyStruct" });
+
+        var func = () => methodInfo.Invoke(instance, [action, new Context(), CancellationToken.None]);
+
+        var exceptionAssertions = func.Should().Throw<TargetInvocationException>();
+        exceptionAssertions.And.Message.Should().Be("Exception has been thrown by the target of an invocation.");
+        exceptionAssertions.And.InnerException.Should().BeOfType<ArgumentNullException>()
+            .Which.ParamName.Should().Be("action");
+    }
+
     [Fact]
     public void Should_throw_when_fallback_action_is_null()
     {