Fix nullability warnings

Author: sandermvanvliet

src/Serilog.Enrichers.Sensitive/SensitiveArea.cs

@@ -5,9 +5,9 @@ namespace Serilog.Enrichers.Sensitive
 {
     public class SensitiveArea : IDisposable
     {
-        private static readonly AsyncLocal<SensitiveArea> InstanceLocal = new AsyncLocal<SensitiveArea>();
+        private static readonly AsyncLocal<SensitiveArea?> InstanceLocal = new();
 
-        public static SensitiveArea Instance
+        public static SensitiveArea? Instance
         {
             get => InstanceLocal.Value;
             set => InstanceLocal.Value = value;

src/Serilog.Enrichers.Sensitive/SensitiveDataEnricher.cs

@@ -21,7 +21,7 @@ internal class SensitiveDataEnricher : ILogEventEnricher
         private readonly List<string> _excludeProperties;
 
         public SensitiveDataEnricher(
-            Action<SensitiveDataEnricherOptions> options)
+            Action<SensitiveDataEnricherOptions>? options)
         {
             var enricherOptions = new SensitiveDataEnricherOptions();
 
@@ -39,12 +39,19 @@ public SensitiveDataEnricher(
             _maskValue = enricherOptions.MaskValue;
             _maskProperties = enricherOptions.MaskProperties ?? new List<string>();
             _excludeProperties = enricherOptions.ExcludeProperties ?? new List<string>();
+            _maskingOperators = enricherOptions.MaskingOperators.ToList();
 
             var fields = typeof(LogEvent).GetFields(BindingFlags.Instance | BindingFlags.NonPublic);
 
-            _messageTemplateBackingField = fields.SingleOrDefault(f => f.Name.Contains("<MessageTemplate>"));
+            var backingField = fields.SingleOrDefault(f => f.Name.Contains("<MessageTemplate>"));
+            
+            if (backingField == null)
+            {
+                throw new InvalidOperationException(
+                    "Could not find the backing field for the message template on the LogEvent type");
+            }
 
-            _maskingOperators = enricherOptions.MaskingOperators.ToList();
+            _messageTemplateBackingField = backingField;
         }
 
         public SensitiveDataEnricher(
@@ -83,7 +90,7 @@ public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
                             .AddOrUpdateProperty(
                                 new LogEventProperty(
                                     property.Key,
-                                    maskedValue));
+                                    maskedValue!));
                     }
                 }
             }
@@ -125,7 +132,7 @@ public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
                             if (wasMasked)
                             {
                                 anyMasked = true;
-                                propList.Add(new LogEventProperty(prop.Name, maskedValue));
+                                propList.Add(new LogEventProperty(prop.Name, maskedValue!));
                             }
                             else
                             {

test/Serilog.Enrichers.Sensitive.Tests.Unit/WhenMaskingWithCustomMaskValue.cs

@@ -12,7 +12,7 @@ public class WhenMaskingWithCustomMaskValue
         public void GivenMaskValueIsNull_ArgumentNullExceptionIsThrown()
         {
             Action action = () => new LoggerConfiguration()
-                .Enrich.WithSensitiveDataMasking(options => options.MaskValue = null)
+                .Enrich.WithSensitiveDataMasking(options => options.MaskValue = null!)
                 .CreateLogger();
 
             action

test/Serilog.Enrichers.Sensitive.Tests.Unit/WhenMaskingWithRegexOperator.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Text.RegularExpressions;
 using FluentAssertions;
 using Xunit;
 
@@ -18,7 +17,7 @@ public RegexExtenderWithOptions(string regexPattern) : base(regexPattern)
 		[Fact]
 		public void GivenConstructor_NullPatternThrowsException()
 		{
-			var ex = Record.Exception(() => new RegexExtenderWithOptions(null));
+			var ex = Record.Exception(() => new RegexExtenderWithOptions(null!));
 			ex
 				.Should()
 				.NotBeNull()