Add nullable annotation to LoggerFilterRule (cherry-pick PR #125897)

Author: ggailey777

articles/azure-functions/dotnet-isolated-process-guide.md

@@ -122,7 +122,7 @@ builder.Logging.Services.Configure<LoggerFilterOptions>(options =>
     {
         // The Application Insights SDK adds a default logging filter that instructs ILogger to capture only Warning and more severe logs. Application Insights requires an explicit override.
         // Log levels can also be configured using appsettings.json. For more information, see https://learn.microsoft.com/azure/azure-monitor/app/worker-service#ilogger-logs
-        LoggerFilterRule defaultRule = options.Rules.FirstOrDefault(rule => rule.ProviderName
+        LoggerFilterRule? defaultRule = options.Rules.FirstOrDefault(rule => rule.ProviderName
             == "Microsoft.Extensions.Logging.ApplicationInsights.ApplicationInsightsLoggerProvider");
         if (defaultRule is not null)
         {
@@ -1008,7 +1008,7 @@ builder.Services
 
 builder.Logging.Services.Configure<LoggerFilterOptions>(options =>
     {
-        LoggerFilterRule defaultRule = options.Rules.FirstOrDefault(rule => rule.ProviderName
+        LoggerFilterRule? defaultRule = options.Rules.FirstOrDefault(rule => rule.ProviderName
             == "Microsoft.Extensions.Logging.ApplicationInsights.ApplicationInsightsLoggerProvider");
         if (defaultRule is not null)
         {
@@ -1039,7 +1039,7 @@ var host = new HostBuilder()
     {
         logging.Services.Configure<LoggerFilterOptions>(options =>
         {
-            LoggerFilterRule defaultRule = options.Rules.FirstOrDefault(rule => rule.ProviderName
+            LoggerFilterRule? defaultRule = options.Rules.FirstOrDefault(rule => rule.ProviderName
                 == "Microsoft.Extensions.Logging.ApplicationInsights.ApplicationInsightsLoggerProvider");
             if (defaultRule is not null)
             {