Fix NullReference in Dictionary + tests Issue #31 (#33)

Author: jtorvald

src/Dahomey.Cbor.Tests/Issues/Issue0031.cs

@@ -15,7 +15,12 @@ public class ObjectWithNullLists
             public List<string> Items { get; set; }
         }
 
-        [Fact]
+		public class ObjectWithNullDictionary
+		{
+			public Dictionary<string, string> Items { get; set; }
+		}
+
+		[Fact]
         public void TestNullReferenceList()
         {
 
@@ -33,7 +38,7 @@ public void TestNullReferenceList()
 
         }
 
-        [Fact]
+		[Fact]
         public void TestNullReferenceArray()
         {
 
@@ -50,5 +55,22 @@ public void TestNullReferenceArray()
             Assert.Equal("A1654279746573F6", hexResult);
         }
 
-    }
+
+		[Fact]
+		public void TestNullReferenceDictionary()
+		{
+			var obj = new ObjectWithNullDictionary();
+
+			string hexResult = null;
+
+			var ex = Record.Exception(() => {
+				hexResult = Helper.Write(obj);
+			});
+
+			Assert.NotEmpty(hexResult);
+			Assert.Null(ex);
+			Assert.Equal("A1654974656D73F6", hexResult);
+
+		}
+	}
 }

src/Dahomey.Cbor/Serialization/Converters/AbstractDictionaryConverter.cs

@@ -45,6 +45,11 @@ public override TC Read(ref CborReader reader)
 
         public override void Write(ref CborWriter writer, TC value)
         {
+            if (value == null)
+            {
+                writer.WriteNull();
+                return;
+            }
             WriterContext context = new WriterContext
             {
                 count = value.Count,