Add tests for nullable keys

Author: Tasteful

src/AutoMapper.Collection.Tests/NullableIdTests.cs

@@ -0,0 +1,51 @@
+using System.Collections.Generic;
+using AutoMapper.EquivalencyExpression;
+using FluentAssertions;
+using Xunit;
+
+namespace AutoMapper.Collection
+{
+    public class NullableIdTests
+    {
+        [Fact]
+        public void Should_Work_With_Null_Id()
+        {
+            Mapper.Reset();
+            Mapper.Initialize(x =>
+            {
+                x.AddCollectionMappers();
+                x.CreateMap<ThingWithStringIdDto, ThingWithStringId>().EqualityComparison((dto, entity) => dto.ID == entity.ID);
+            });
+
+            var original = new List<ThingWithStringId>
+            {
+                new ThingWithStringId { ID = "1", Title = "test0" },
+                new ThingWithStringId { ID = "2", Title = "test2" },
+            };
+
+            var dtos = new List<ThingWithStringIdDto>
+            {
+                new ThingWithStringIdDto { ID = "1", Title = "test0" },
+                new ThingWithStringIdDto { ID = "2", Title = "test2" },
+                new ThingWithStringIdDto { Title = "test3" }
+            };
+
+            Mapper.Map(dtos, original);
+
+            original.Should().HaveSameCount(dtos);
+        }
+
+        public class ThingWithStringId
+        {
+            public string ID { get; set; }
+            public string Title { get; set; }
+            public override string ToString() { return Title; }
+        }
+
+        public class ThingWithStringIdDto
+        {
+            public string ID { get; set; }
+            public string Title { get; set; }
+        }
+    }
+}