Fix NullReferenceException when calling AddFluentValidationClientsideAdapters (#1969)

Author: JeremySkinner

src/Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <VersionPrefix>11.1.0</VersionPrefix>
+    <VersionPrefix>11.1.1</VersionPrefix>
     <VersionSuffix></VersionSuffix>
     <!-- Use CI build number as version suffix (if defined) -->
     <!--<VersionSuffix Condition="'$(GITHUB_RUN_NUMBER)'!=''">ci-$(GITHUB_RUN_NUMBER)</VersionSuffix>-->

src/FluentValidation.AspNetCore/FluentValidationMvcExtensions.cs

@@ -167,7 +167,7 @@ public FluentValidationViewOptionsSetup(Action<FluentValidationClientModelValida
 
 		public void Configure(MvcViewOptions options) {
 			var provider = new FluentValidationClientModelValidatorProvider(_httpContextAccessor);
-			_action(provider);
+			_action?.Invoke(provider);
 			options.ClientModelValidatorProviders.Add(provider);
 		}
 	}