Updated extensions to account for nulls

Also added unit tests for these scenarios

Author: grofit

src/SystemsRx.Tests/SystemsRx/Extensions/IDictionaryExtensionTests.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using NSubstitute;
+using SystemsRx.Extensions;
+using Xunit;
+
+namespace SystemsRx.Tests.SystemsRx.Extensions
+{
+    public class IDictionaryExtensionTests
+    {
+        [Fact]
+        public void should_work_with_nulls_and_disposables_individually()
+        {
+            var mockDisposable1 = Substitute.For<IDisposable>();
+            var mockDisposable2 = Substitute.For<IDisposable>();
+            
+            var dictionary = new Dictionary<int, IDisposable>
+            {
+                { 1, null },
+                { 2, mockDisposable1 },
+                { 3, null },
+                { 4, mockDisposable2 }
+            };
+            
+            dictionary.RemoveAndDispose(1);
+            dictionary.RemoveAndDispose(2);
+            dictionary.RemoveAndDispose(3);
+            dictionary.RemoveAndDispose(4);
+            
+            Assert.Empty(dictionary);
+            mockDisposable1.Received(1).Dispose();
+            mockDisposable2.Received(1).Dispose();
+        }
+        
+        [Fact]
+        public void should_work_with_nulls_and_disposables()
+        {
+            var mockDisposable1 = Substitute.For<IDisposable>();
+            var mockDisposable2 = Substitute.For<IDisposable>();
+            
+            var dictionary = new Dictionary<int, IDisposable>
+            {
+                { 1, null },
+                { 2, mockDisposable1 },
+                { 3, null },
+                { 4, mockDisposable2 }
+            };
+            
+            dictionary.RemoveAndDisposeAll();
+
+            Assert.Empty(dictionary);
+            mockDisposable1.Received(1).Dispose();
+            mockDisposable2.Received(1).Dispose();
+        }
+        
+        [Fact]
+        public void should_work_with_nulls_and_disposables_in_enumerable()
+        {
+            var mockDisposable1 = Substitute.For<IDisposable>();
+            var mockDisposable2 = Substitute.For<IDisposable>();
+
+            var collection = new[]
+            {
+                null,
+                mockDisposable1,
+                null,
+                mockDisposable2
+            };
+            
+            collection.DisposeAll();
+
+            Assert.Equal(4, collection.Length);
+            mockDisposable1.Received(1).Dispose();
+            mockDisposable2.Received(1).Dispose();
+        }
+    }
+}

src/SystemsRx/Extensions/IDictionaryExtensions.cs

@@ -7,13 +7,14 @@ public static class IDictionaryExtensions
     {       
         public static void RemoveAndDispose<T>(this IDictionary<T, IDisposable> disposables, T key)
         {
-            disposables[key].Dispose();
+            var disposable = disposables[key];
             disposables.Remove(key);
+            disposable?.Dispose();
         }
 
         public static void RemoveAndDisposeAll<T>(this IDictionary<T, IDisposable> disposables)
         {
-            disposables.ForEachRun(x => x.Value.Dispose());
+            disposables.ForEachRun(x => x.Value?.Dispose());
             disposables.Clear();
         }
     }

src/SystemsRx/Extensions/IDisposableExtensions.cs

@@ -8,13 +8,13 @@ public static class IDisposableExtensions
         public static void DisposeAll(this IEnumerable<IDisposable> disposables)
         {
             foreach(var disposable in disposables)
-            { disposable.Dispose(); }
+            { disposable?.Dispose(); }
         }
 
         public static void DisposeAll<T>(this IDictionary<T, IDisposable> disposables)
         {
             foreach(var disposable in disposables.Values)
-            { disposable.Dispose(); }
+            { disposable?.Dispose(); }
         }
 
         public static IDisposable AddTo(this IDisposable currentDisposable, ICollection<IDisposable> disposables)