Warning if not using 'is not null'

.editorconfig

@@ -121,8 +121,10 @@ csharp_space_between_method_declaration_name_and_open_parenthesis = false
 csharp_space_between_method_declaration_parameter_list_parentheses = false
 csharp_space_between_parentheses = false
 csharp_space_between_square_brackets = false
+csharp_style_prefer_null_check_over_type_check = true:warning
 
 # C++ Files
+
 [*.{cpp,h,in}]
 curly_bracket_next_line = true
 indent_brace_style = Allman

BTCPayServer.Client/JsonConverters/NodeUriJsonConverter.cs

@@ -19,7 +19,7 @@ namespace BTCPayServer.Client.JsonConverters
 
         public override void WriteJson(JsonWriter writer, [AllowNull] NodeInfo value, JsonSerializer serializer)
         {
-            if (value is NodeInfo)
+            if (value is not null)
                 writer.WriteValue(value.ToString());
         }
     }

BTCPayServer.Rating/Providers/BackgroundFetcherRateProvider.cs

@@ -95,7 +95,7 @@ namespace BTCPayServer.Services.Rates
             {
                 LastRequested = LastRequested
             };
-            if (_Latest is LatestFetch fetch && fetch.Latest is PairRate[])
+            if (_Latest is LatestFetch fetch && fetch.Latest is not null)
             {
                 state.LastUpdated = fetch.Updated;
                 state.Rates = fetch.Latest

BTCPayServer.Tests/SeleniumTester.cs

@@ -479,7 +479,7 @@ namespace BTCPayServer.Tests
             currencyEl.Clear();
             currencyEl.SendKeys(currency);
             Driver.FindElement(By.Id("BuyerEmail")).SendKeys(refundEmail);
-            if (defaultPaymentMethod is string)
+            if (defaultPaymentMethod is not null)
                 new SelectElement(Driver.FindElement(By.Name("DefaultPaymentMethod"))).SelectByValue(defaultPaymentMethod);
             if (requiresRefundEmail is bool)
                 new SelectElement(Driver.FindElement(By.Name("RequiresRefundEmail"))).SelectByValue(requiresRefundEmail == true ? "1" : "2");

BTCPayServer/Controllers/UIInvoiceController.UI.cs

@@ -500,21 +500,21 @@ namespace BTCPayServer.Controllers
                 var enabledPaymentIds = store.GetEnabledPaymentIds(_NetworkProvider);
                 PaymentMethodId? invoicePaymentId = invoice.GetDefaultPaymentMethod();
                 PaymentMethodId? storePaymentId = store.GetDefaultPaymentId();
-                if (invoicePaymentId is PaymentMethodId)
+                if (invoicePaymentId is not null)
                 {
                     if (enabledPaymentIds.Contains(invoicePaymentId))
                         paymentMethodId = invoicePaymentId;
                 }
-                if (paymentMethodId is null && storePaymentId is PaymentMethodId)
+                if (paymentMethodId is null && storePaymentId is not null)
                 {
                     if (enabledPaymentIds.Contains(storePaymentId))
                         paymentMethodId = storePaymentId;
                 }
-                if (paymentMethodId is null && invoicePaymentId is PaymentMethodId)
+                if (paymentMethodId is null && invoicePaymentId is not null)
                 {
                     paymentMethodId = invoicePaymentId.FindNearest(enabledPaymentIds);
                 }
-                if (paymentMethodId is null && storePaymentId is PaymentMethodId)
+                if (paymentMethodId is null && storePaymentId is not null)
                 {
                     paymentMethodId = storePaymentId.FindNearest(enabledPaymentIds);
                 }

BTCPayServer/Controllers/UIStoresController.cs

@@ -419,7 +419,7 @@ namespace BTCPayServer.Controllers
         {
             var enabled = storeData.GetEnabledPaymentIds(_NetworkProvider);
             var defaultPaymentId = storeData.GetDefaultPaymentId();
-            var defaultChoice = defaultPaymentId is PaymentMethodId ? defaultPaymentId.FindNearest(enabled) : null;
+            var defaultChoice = defaultPaymentId is not null ? defaultPaymentId.FindNearest(enabled) : null;
             if (defaultChoice is null)
             {
                 defaultChoice = enabled.FirstOrDefault(e => e.CryptoCode == "BTC" && e.PaymentType == PaymentTypes.BTCLike) ??

BTCPayServer/Extensions/ControllerBaseExtensions.cs

@@ -40,7 +40,7 @@ namespace BTCPayServer
             // but we want searchTerm to be null only if the user is browsing the page via some link
             // NOT if the user entered some empty search
             var searchTerm = model.SearchTerm;
-            searchTerm = searchTerm is string ? searchTerm :
+            searchTerm = searchTerm is not null ? searchTerm :
                          ctrl.Request.Query.ContainsKey(nameof(searchTerm)) ? string.Empty :
                          null;
             if (searchTerm is null)

BTCPayServer/HostedServices/WebhookSender.cs

@@ -254,7 +254,7 @@ namespace BTCPayServer.HostedServices
                 var result = await SendAndSaveDelivery(ctx, cancellationToken);
                 if (ctx.WebhookBlob.AutomaticRedelivery &&
                     !result.Success &&
-                    result.DeliveryId is string)
+                    result.DeliveryId is not null)
                 {
                     var originalDeliveryId = result.DeliveryId;
                     foreach (var wait in new[]

BTCPayServer/Security/GreenField/APIKeyExtensions.cs

@@ -58,7 +58,7 @@ namespace BTCPayServer.Security.Greenfield
             {
                 if (Permission.TryParse(claim.Value, out var claimPermission))
                 {
-                    if (requireUnscoped && claimPermission.Scope is string)
+                    if (requireUnscoped && claimPermission.Scope is not null)
                         continue;
                     if (claimPermission.Contains(permission))
                     {