added null handling for DictionaryExtension method (#1036)

src/SimplCommerce.Infrastructure/Extensions/DictionaryExtensions.cs

@@ -24,7 +24,7 @@ internal static bool TryGetValue<T>(this IDictionary<string, object> dictionary,
                 return true;
             }
 
-            value = default(T);
+            value = default;
             return false;
         }
 
@@ -38,7 +38,9 @@ internal static bool TryGetValue<T>(this IDictionary<string, object> dictionary,
         /// <returns>Value if found, default if can not found.</returns>
         public static TValue GetOrDefault<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key)
         {
-            return dictionary.TryGetValue(key, out var obj) ? obj : default(TValue);
+            if (dictionary != null)
+                return dictionary.TryGetValue(key, out var obj) ? obj : default;
+            return default;
         }
 
         /// <summary>

test/SimplCommerce.Infrastructure.Tests/Extensions/DictionaryExtensionsTests.cs

@@ -0,0 +1,31 @@
+using System.Collections.Generic;
+using SimplCommerce.Infrastructure.Extensions;
+using Xunit;
+
+namespace SimplCommerce.Infrastructure.Tests
+{
+    public class DictionaryExtensionsTests
+    {
+        internal class MockClass
+        {
+        }
+
+        [Fact]
+        public void GetOrDefaultShouldReturnDefaultWithNullDictionary()
+        {
+            Dictionary<string, MockClass> dict = null;
+            MockClass result = dict.GetOrDefault("key");
+            Assert.Null(result);
+        }
+
+        [Fact]
+        public void GetOrDefaultShouldReturnCorrectValue()
+        {
+            MockClass mockClass = new MockClass();
+            Dictionary<string, MockClass> dict = new Dictionary<string, MockClass> { { "key", mockClass } };
+            MockClass result = dict.GetOrDefault("key");
+            Assert.NotNull(result);
+            Assert.Equal(mockClass, result);
+        }
+    }
+}