Enable nullable reference types

Directory.Build.props

@@ -1,7 +1,23 @@
 <Project>
 
-   <PropertyGroup>
-      <EnforceCodeStyleInBuild>True</EnforceCodeStyleInBuild>
-   </PropertyGroup>
+    <PropertyGroup>
+        <EnforceCodeStyleInBuild>True</EnforceCodeStyleInBuild>
+    </PropertyGroup>
 
-</Project>
+    <PropertyGroup>
+        <Nullable>enable</Nullable>
+        <WarningsAsErrors>nullable</WarningsAsErrors>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="Nullable" Version="1.3.1">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+        <PackageReference Include="Required" Version="1.0.0">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+</Project>

examples/ConfigStoreDemo/Pages/About.cshtml.cs

@@ -7,7 +7,7 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Examples.Conf
 {
     public class AboutModel : PageModel
     {
-        public string Message { get; set; }
+        public string? Message { get; set; }
 
         public void OnGet()
         {

examples/ConfigStoreDemo/Pages/Contact.cshtml.cs

@@ -7,7 +7,7 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Examples.Conf
 {
     public class ContactModel : PageModel
     {
-        public string Message { get; set; }
+        public string? Message { get; set; }
 
         public void OnGet()
         {

examples/ConfigStoreDemo/Pages/Error.cshtml.cs

@@ -8,7 +8,7 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Examples.Conf
 {
     public class ErrorModel : PageModel
     {
-        public string RequestId { get; set; }
+        public string? RequestId { get; set; }
 
         public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
 

examples/ConfigStoreDemo/Program.cs

@@ -26,7 +26,13 @@ public static IWebHost BuildWebHost(string[] args)
                     var settings = config.AddJsonFile("appsettings.json").Build();
                     config.AddAzureAppConfiguration(options =>
                     {
-                        options.Connect(settings["connection_string"])
+                        var connectionString = settings["connection_string"];
+                        if (string.IsNullOrEmpty(connectionString))
+                        {
+                            throw new InvalidOperationException("Connection string not found");
+                        }
+
+                        options.Connect(connectionString)
                                .ConfigureRefresh(refresh =>
                                {
                                    refresh.Register("Settings:BackgroundColor")

examples/ConfigStoreDemo/Settings.cs

@@ -5,12 +5,12 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Examples.Conf
 {
     public class Settings
     {
-        public string AppName { get; set; }
+        public string? AppName { get; set; }
         public double Version { get; set; }
         public long RefreshRate { get; set; }
         public long FontSize { get; set; }
-        public string Language { get; set; }
-        public string Messages { get; set; }
-        public string BackgroundColor { get; set; }
+        public string? Language { get; set; }
+        public string? Messages { get; set; }
+        public string? BackgroundColor { get; set; }
     }
 }

examples/ConsoleAppWithFailOver/Program.cs

@@ -11,7 +11,7 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Examples.Cons
 {
     class Program
     {
-        static IConfiguration Configuration { get; set; }
+        static IConfiguration? Configuration { get; set; }
 
         static void Main(string[] args)
         {
@@ -31,7 +31,7 @@ private static void Configure()
             IConfiguration configuration = builder.Build();
 
             IConfigurationSection endpointsSection = configuration.GetSection("AppConfig:Endpoints");
-            IEnumerable<Uri> endpoints = endpointsSection.GetChildren().Select(endpoint => new Uri(endpoint.Value));
+            IEnumerable<Uri> endpoints = endpointsSection.GetChildren().Select(endpoint => new Uri(endpoint.Value!));
 
             if (endpoints == null || !endpoints.Any())
             {

examples/ConsoleApplication/Program.cs

@@ -6,14 +6,15 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Examples.Cons
     using Microsoft.Extensions.Configuration;
     using Microsoft.Extensions.Configuration.AzureAppConfiguration;
     using System;
+    using System.Diagnostics.CodeAnalysis;
     using System.Text;
     using System.Threading;
     using System.Threading.Tasks;
 
     class Program
     {
-        static IConfiguration Configuration { get; set; }
-        static IConfigurationRefresher _refresher;
+        static IConfiguration? Configuration { get; set; }
+        static IConfigurationRefresher? _refresher;
 
         static void Main(string[] args)
         {
@@ -28,6 +29,7 @@ static void Main(string[] args)
             cts.Cancel();
         }
 
+        [MemberNotNull(nameof(Configuration))]
         private static void Configure()
         {
             var builder = new ConfigurationBuilder();
@@ -38,18 +40,18 @@ private static void Configure()
 
             IConfiguration configuration = builder.Build();
 
-            if (string.IsNullOrEmpty(configuration["connection_string"]))
+            var connectionString = configuration["connection_string"];
+            if (string.IsNullOrEmpty(connectionString))
             {
-                Console.WriteLine("Connection string not found.");
                 Console.WriteLine("Please set the 'connection_string' environment variable to a valid Azure App Configuration connection string and re-run this example.");
-                return;
+                throw new InvalidOperationException("Connection string not found");
             }
 
             // Augment the configuration builder with Azure App Configuration
             // Pull the connection string from an environment variable
             builder.AddAzureAppConfiguration(options =>
             {
-                options.Connect(configuration["connection_string"])
+                options.Connect(connectionString)
                        .Select("AppName")
                        .Select("Settings:BackgroundColor")
                        .ConfigureClientOptions(clientOptions => clientOptions.Retry.MaxRetries = 5)
@@ -75,9 +77,9 @@ private static async Task Run(CancellationToken token)
             while (!token.IsCancellationRequested)
             {
                 // Trigger an async refresh for registered configuration settings without wait
-                _ = _refresher.TryRefreshAsync();
+                _ = _refresher!.TryRefreshAsync();
 
-                sb.AppendLine($"{Configuration["AppName"]} has been configured to run in {Configuration["Language"]}");
+                sb.AppendLine($"{Configuration!["AppName"]} has been configured to run in {Configuration["Language"]}");
                 sb.AppendLine();
 
                 sb.AppendLine(string.Equals(Configuration["Language"], "spanish", StringComparison.OrdinalIgnoreCase) ? "Buenos Dias." : "Good morning");

src/Microsoft.Azure.AppConfiguration.AspNetCore/AzureAppConfigurationRefreshExtensions.cs

@@ -25,7 +25,7 @@ public static IApplicationBuilder UseAzureAppConfiguration(this IApplicationBuil
                 throw new ArgumentNullException(nameof(builder));
             }
 
-            IConfigurationRefresherProvider refresherProvider = (IConfigurationRefresherProvider)builder.ApplicationServices.GetService(typeof(IConfigurationRefresherProvider));
+            IConfigurationRefresherProvider? refresherProvider = (IConfigurationRefresherProvider?)builder.ApplicationServices.GetService(typeof(IConfigurationRefresherProvider));
 
             // Verify if AddAzureAppConfiguration was done before calling UseAzureAppConfiguration.
             // We use the IConfigurationRefresherProvider to make sure if the required services were added.

src/Microsoft.Azure.AppConfiguration.Functions.Worker/AzureAppConfigurationRefreshExtensions.cs

@@ -24,7 +24,7 @@ public static class AzureAppConfigurationRefreshExtensions
         public static IFunctionsWorkerApplicationBuilder UseAzureAppConfiguration(this IFunctionsWorkerApplicationBuilder builder)
         {
             IServiceProvider serviceProvider = builder.Services.BuildServiceProvider();
-            IConfigurationRefresherProvider refresherProvider = serviceProvider.GetService<IConfigurationRefresherProvider>();
+            IConfigurationRefresherProvider? refresherProvider = serviceProvider.GetService<IConfigurationRefresherProvider>();
 
             // Verify if AddAzureAppConfiguration was done before calling UseAzureAppConfiguration.
             // We use the IConfigurationRefresherProvider to make sure if the required services were added.

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationKeyVaultOptions.cs

@@ -5,6 +5,7 @@
 using Azure.Security.KeyVault.Secrets;
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
 
 namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
@@ -14,10 +15,10 @@ namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
     /// </summary>
     public class AzureAppConfigurationKeyVaultOptions
     {
-        internal TokenCredential Credential;
+        internal TokenCredential? Credential;
         internal SecretClientOptions ClientOptions = new SecretClientOptions();
         internal List<SecretClient> SecretClients = new List<SecretClient>();
-        internal Func<Uri, ValueTask<string>> SecretResolver;
+        internal Func<Uri, ValueTask<string>>? SecretResolver;
         internal Dictionary<string, TimeSpan> SecretRefreshIntervals = new Dictionary<string, TimeSpan>();
         internal TimeSpan? DefaultSecretRefreshInterval = null;
         internal bool IsKeyVaultRefreshConfigured = false;
@@ -26,6 +27,7 @@ public class AzureAppConfigurationKeyVaultOptions
         /// Sets the credentials used to authenticate to key vaults that have no registered <see cref="SecretClient"/>.
         /// </summary>
         /// <param name="credential">Default token credentials.</param>
+        [MemberNotNull(nameof(Credential))]
         public AzureAppConfigurationKeyVaultOptions SetCredential(TokenCredential credential)
         {
             Credential = credential;
@@ -57,6 +59,7 @@ public AzureAppConfigurationKeyVaultOptions Register(SecretClient secretClient)
         /// Sets the callback used to resolve key vault references that have no registered <see cref="SecretClient"/>.
         /// </summary>
         /// <param name="secretResolver">A callback that maps the <see cref="Uri"/> of the key vault secret to its value.</param>
+        [MemberNotNull(nameof(SecretResolver))]
         public AzureAppConfigurationKeyVaultOptions SetSecretResolver(Func<Uri, ValueTask<string>> secretResolver)
         {
             if (secretResolver == null)

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationOptions.cs

@@ -42,19 +42,19 @@ public class AzureAppConfigurationOptions
         /// <summary>
         /// The list of connection strings used to connect to an Azure App Configuration store and its replicas.
         /// </summary>
-        internal IEnumerable<string> ConnectionStrings { get; private set; }
+        internal IEnumerable<string>? ConnectionStrings { get; private set; }
 
         /// <summary>
         /// The list of endpoints of an Azure App Configuration store.
         /// If this property is set, the <see cref="Credential"/> property also needs to be set.
         /// </summary>
-        internal IEnumerable<Uri> Endpoints { get; private set; }
+        internal IEnumerable<Uri>? Endpoints { get; private set; }
 
         /// <summary>
         /// The credential used to connect to the Azure App Configuration.
         /// If this property is set, the <see cref="Endpoints"/> property also needs to be set.
         /// </summary>
-        internal TokenCredential Credential { get; private set; }
+        internal TokenCredential? Credential { get; private set; }
 
         /// <summary>
         /// A collection of <see cref="KeyValueSelector"/>.
@@ -77,7 +77,7 @@ public class AzureAppConfigurationOptions
         internal IEnumerable<IKeyValueAdapter> Adapters
         {
             get => _adapters;
-            set => _adapters = value?.ToList();
+            set => _adapters = value.ToList();
         }
 
         /// <summary>
@@ -94,7 +94,7 @@ internal IEnumerable<IKeyValueAdapter> Adapters
         /// An optional configuration client manager that can be used to provide clients to communicate with Azure App Configuration.
         /// </summary>
         /// <remarks>This property is used only for unit testing.</remarks>
-        internal IConfigurationClientManager ClientManager { get; set; }
+        internal IConfigurationClientManager? ClientManager { get; set; }
 
         /// <summary>
         /// An optional timespan value to set the minimum backoff duration to a value other than the default.
@@ -158,7 +158,7 @@ public AzureAppConfigurationOptions()
         /// The label filter to apply when querying Azure App Configuration for key-values. By default the null label will be used. Built-in label filter options: <see cref="LabelFilter"/>
         /// The characters asterisk (*) and comma (,) are not supported. Backslash (\) character is reserved and must be escaped using another backslash (\).
         /// </param>
-        public AzureAppConfigurationOptions Select(string keyFilter, string labelFilter = LabelFilter.Null)
+        public AzureAppConfigurationOptions Select(string keyFilter, string? labelFilter = LabelFilter.Null)
         {
             if (string.IsNullOrEmpty(keyFilter))
             {
@@ -177,10 +177,10 @@ public AzureAppConfigurationOptions Select(string keyFilter, string labelFilter
             }
 
             _kvSelectors.AppendUnique(new KeyValueSelector
-            {
-                KeyFilter = keyFilter,
-                LabelFilter = labelFilter
-            });
+            (
+                keyFilter: keyFilter,
+                labelFilter: labelFilter!
+            ));
             return this;
         }
 
@@ -196,10 +196,7 @@ public AzureAppConfigurationOptions SelectSnapshot(string name)
                 throw new ArgumentNullException(nameof(name));
             }
 
-            _kvSelectors.AppendUnique(new KeyValueSelector
-            {
-                SnapshotName = name
-            });
+            _kvSelectors.AppendUnique(new KeyValueSelector(snapshotName: name));
 
             return this;
         }
@@ -210,7 +207,7 @@ public AzureAppConfigurationOptions SelectSnapshot(string name)
         /// All loaded feature flags will be automatically registered for refresh on an individual flag level.
         /// </summary>
         /// <param name="configure">A callback used to configure feature flag options.</param>
-        public AzureAppConfigurationOptions UseFeatureFlags(Action<FeatureFlagOptions> configure = null)
+        public AzureAppConfigurationOptions UseFeatureFlags(Action<FeatureFlagOptions>? configure = null)
         {
             FeatureFlagOptions options = new FeatureFlagOptions();
             configure?.Invoke(options);
@@ -230,23 +227,23 @@ public AzureAppConfigurationOptions UseFeatureFlags(Action<FeatureFlagOptions> c
             {
                 // Select clause is not present
                 options.FeatureFlagSelectors.Add(new KeyValueSelector
-                {
-                    KeyFilter = FeatureManagementConstants.FeatureFlagMarker + "*",
-                    LabelFilter = options.Label == null ? LabelFilter.Null : options.Label
-                });
+                (
+                    keyFilter: FeatureManagementConstants.FeatureFlagMarker + "*",
+                    labelFilter: options.Label == null ? LabelFilter.Null : options.Label
+                ));
             }
 
             foreach (var featureFlagSelector in options.FeatureFlagSelectors)
             {
                 var featureFlagFilter = featureFlagSelector.KeyFilter;
                 var labelFilter = featureFlagSelector.LabelFilter;
 
-                Select(featureFlagFilter, labelFilter);
+                Select(featureFlagFilter!, labelFilter!);
 
                 _multiKeyWatchers.AppendUnique(new KeyValueWatcher
                 {
-                    Key = featureFlagFilter,
-                    Label = labelFilter,
+                    Key = featureFlagFilter!,
+                    Label = labelFilter!,
                     // If UseFeatureFlags is called multiple times for the same key and label filters, last cache expiration time wins
                     CacheExpirationInterval = options.CacheExpirationInterval
                 });