feat: add null checks

Author: phnx47

src/ServiceCollectionExtensions.cs

@@ -1,4 +1,5 @@
-using Microsoft.Extensions.DependencyInjection;
+using System;
+using Microsoft.Extensions.DependencyInjection;
 using Prometheus.Client.Collectors;
 
 namespace Prometheus.Client.DependencyInjection;
@@ -11,6 +12,9 @@ public static class ServiceCollectionExtensions
     /// <param name="services">Service collection</param>
     public static IServiceCollection AddMetricFactory(this IServiceCollection services)
     {
+        if (services == null)
+            throw new ArgumentNullException(nameof(services));
+
         services.AddSingleton<ICollectorRegistry, CollectorRegistry>();
         services.AddSingleton<IMetricFactory, MetricFactory>();
         return services;
@@ -23,6 +27,11 @@ public static IServiceCollection AddMetricFactory(this IServiceCollection servic
     /// <param name="collectorRegistry">Explicit collector registry to use</param>
     public static IServiceCollection AddMetricFactory(this IServiceCollection services, ICollectorRegistry collectorRegistry)
     {
+        if (services == null)
+            throw new ArgumentNullException(nameof(services));
+        if (collectorRegistry == null)
+            throw new ArgumentNullException(nameof(collectorRegistry));
+
         services.AddSingleton(collectorRegistry);
         services.AddSingleton<IMetricFactory, MetricFactory>();
         return services;

tests/ServiceCollectionExtensionsTests.cs

@@ -1,3 +1,4 @@
+using System;
 using Microsoft.Extensions.DependencyInjection;
 using Prometheus.Client.Collectors;
 using Xunit;
@@ -7,7 +8,7 @@ namespace Prometheus.Client.DependencyInjection.Tests;
 public class ServiceCollectionExtensionsTests
 {
     [Fact]
-    public void Check_AddMetricFactory()
+    public void AddMetricFactory_Default()
     {
         var sp = new ServiceCollection()
             .AddMetricFactory()
@@ -18,7 +19,7 @@ public void Check_AddMetricFactory()
     }
 
     [Fact]
-    public void Check_AddMetricFactory_Custom_CollectorRegistry()
+    public void AddMetricFactory_With_Custom_CollectorRegistry()
     {
         var collectorRegistry = new CollectorRegistry();
 
@@ -35,7 +36,7 @@ public void Check_AddMetricFactory_Custom_CollectorRegistry()
     }
 
     [Fact]
-    public void Check_AddMetricFactory_Default_CollectorRegistry()
+    public void AddMetricFactory_With_Default_CollectorRegistry()
     {
         var sp = new ServiceCollection()
             .AddMetricFactory(Metrics.DefaultCollectorRegistry)
@@ -45,4 +46,23 @@ public void Check_AddMetricFactory_Default_CollectorRegistry()
         Assert.NotNull(metricFactory);
         Assert.Equal(Metrics.DefaultCollectorRegistry, sp.GetService<ICollectorRegistry>());
     }
+
+    [Fact]
+    public void AddMetricFactory_Default_With_Null_ServiceCollection()
+    {
+        Assert.Throws<ArgumentNullException>(() => ((ServiceCollection)null).AddMetricFactory());
+    }
+
+    [Fact]
+    public void AddMetricFactory_With_Null_ServiceCollection()
+    {
+        Assert.Throws<ArgumentNullException>(() => ((ServiceCollection)null).AddMetricFactory(Metrics.DefaultCollectorRegistry));
+    }
+
+    [Fact]
+    public void AddMetricFactory_With_Null_CollectorRegistry()
+    {
+        var sc = new ServiceCollection();
+        Assert.Throws<ArgumentNullException>(() => sc.AddMetricFactory(null));
+    }
 }