Enable nullability annotations

Author: Numpsy

src/Serilog.Settings.AppSettings/AppSettingsLoggerConfigurationExtensions.cs

@@ -39,7 +39,7 @@ public static class AppSettingsLoggerConfigurationExtensions
         /// <returns>An object allowing configuration to continue.</returns>
         [EditorBrowsable(EditorBrowsableState.Never)]
         public static LoggerConfiguration AppSettings(
-            this LoggerSettingsConfiguration settingConfiguration, string settingPrefix)
+            this LoggerSettingsConfiguration settingConfiguration, string? settingPrefix)
         {
             return AppSettings(settingConfiguration, settingPrefix, filePath: null);
         }
@@ -60,10 +60,10 @@ public static LoggerConfiguration AppSettings(
         /// By default, the current application's configuration file will be used.</param>
         /// <returns>An object allowing configuration to continue.</returns>
         public static LoggerConfiguration AppSettings(
-            this LoggerSettingsConfiguration settingConfiguration, string settingPrefix = null, string filePath = null)
+            this LoggerSettingsConfiguration settingConfiguration, string? settingPrefix = null, string? filePath = null)
         {
-            if (settingConfiguration == null) throw new ArgumentNullException(nameof(settingConfiguration));
-            if (settingPrefix != null)
+            if (settingConfiguration is null) throw new ArgumentNullException(nameof(settingConfiguration));
+            if (settingPrefix is not null)
             {
                 if (settingPrefix.Contains(":")) throw new ArgumentException("Custom setting prefixes cannot contain the colon (:) character.");
                 if (settingPrefix == "serilog") throw new ArgumentException("The value \"serilog\" is not a permitted setting prefix. To use the default, do not specify a custom prefix at all.");

src/Serilog.Settings.AppSettings/Serilog.Settings.AppSettings.csproj

@@ -26,6 +26,8 @@
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <DelaySign>false</DelaySign>
+    <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/Serilog.Settings.AppSettings/Settings/AppSettings/AppSettingsSettings.cs

@@ -24,18 +24,18 @@ namespace Serilog.Settings.AppSettings
 {
     class AppSettingsSettings : ILoggerSettings
     {
-        readonly string _filePath;
+        readonly string? _filePath;
         readonly string _settingPrefix;
 
-        public AppSettingsSettings(string settingPrefix = null, string filePath = null)
+        public AppSettingsSettings(string? settingPrefix = null, string? filePath = null)
         {
             _filePath = filePath;
-            _settingPrefix = settingPrefix == null ? "serilog:" : $"{settingPrefix}:serilog:";
+            _settingPrefix = settingPrefix is null ? "serilog:" : $"{settingPrefix}:serilog:";
         }
 
         public void Configure(LoggerConfiguration loggerConfiguration)
         {
-            if (loggerConfiguration == null) throw new ArgumentNullException(nameof(loggerConfiguration));
+            if (loggerConfiguration is null) throw new ArgumentNullException(nameof(loggerConfiguration));
 
             IEnumerable<KeyValuePair<string, string>> settings;
 
@@ -56,7 +56,7 @@ public void Configure(LoggerConfiguration loggerConfiguration)
             else
             {
                 settings = ConfigurationManager.AppSettings.AllKeys
-                    .Select(k => new KeyValuePair<string, string>(k, ConfigurationManager.AppSettings[k]));
+                    .Select(k => new KeyValuePair<string, string>(k, ConfigurationManager.AppSettings[k]!));
             }
 
             var pairs = settings