Fixes GH2626 - removes the null-coallescing assignment operator when …

…processing items in the Enumerable Value Retriever; which forces the EVR to find and use the most appropriate Value Retriever for each item in the list (instead of assuming that each item can be processed by the ValueRetriever found for the first item in the list).

TechTalk.SpecFlow/Assist/ValueRetrievers/EnumerableValueRetriever.cs

@@ -40,7 +40,7 @@ private IEnumerable GetItems(string[] strings, KeyValuePair<string, string> keyV
             foreach (var splitValue in strings)
             {
                 var itemKeyValuePair = new KeyValuePair<string, string>(keyValuePair.Key, splitValue.Trim());
-                retriever ??= GetValueRetriever(itemKeyValuePair, targetType, itemType);
+                retriever = GetValueRetriever(itemKeyValuePair, targetType, itemType);
                 yield return retriever?.Retrieve(itemKeyValuePair, targetType, itemType);
             }
         }

Tests/TechTalk.SpecFlow.RuntimeTests/AssistTests/SituationalTests/ListOfNullablesWithCustomNullValueRetrieverTests.cs

@@ -0,0 +1,78 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using FluentAssertions;
+using TechTalk.SpecFlow.Assist;
+using TechTalk.SpecFlow.Assist.ValueRetrievers;
+using TechTalk.SpecFlow.RuntimeTests.AssistTests.ValueRetrieverTests;
+using Xunit;
+
+
+namespace TechTalk.SpecFlow.RuntimeTests.AssistTests.SituationalTests.EnumberableValueRetrieverIntegrationTests
+{
+    public class Example
+    {
+        public IList<int?> MyExampleValues { get; set; }
+
+    }
+
+    public class ListOfNullablesWithCustomNullValueRetrieverTests
+    {
+
+        private const string Val = "1, <null>";
+        private TableRow testRow = new TableRow(new Table("Value"), new string[] {"list", Val});
+
+        [Fact]
+        public void CanRetrieveAListThatContainsValuesThatShouldBeRetrievedByACustomValueRetriever()
+        {
+            Service.Instance.ValueRetrievers.Register(new NullValueRetriever("<null>"));
+
+            var retriever_under_test = Service.Instance.GetValueRetrieverFor(testRow, typeof(object), typeof(IList<Nullable<int>>));
+            retriever_under_test.Should().NotBeNull();
+
+            var can = retriever_under_test.CanRetrieve(Val, typeof(IList<Nullable<int>>));
+
+            can.Should().BeTrue();
+
+            var returned_list = retriever_under_test.Retrieve(new KeyValuePair<string, string>("Value", Val), typeof(object), typeof(IList<Nullable<int>>));
+
+            returned_list.Should().NotBeNull();
+
+            var listOfNullableInts = returned_list as IList<Nullable<int>>;
+
+            listOfNullableInts.Should().NotBeNull();
+
+            listOfNullableInts.Count.Should().Be(2);
+
+            listOfNullableInts[0].Should().Be(1);
+            listOfNullableInts[1].Should().BeNull();
+
+        }
+
+        public static IEnumerable<object[]> EnumerableRetrieverWithNullableValueRetriever_TestCases() =>
+            new List<object[]>
+            {
+                new object[] { "1, 2", new List<int?> {1, 2 } },
+                new object[] { "1, <null>", new List<int?> { 1, null} },
+                new object[] { "<null>, 2", new List<int?> { null, 2} }
+            };
+
+        [Theory]
+        [MemberData(nameof(EnumerableRetrieverWithNullableValueRetriever_TestCases))]
+        public void IntegrationOfEnumerableRetrieverWithNullableValueRetriever(string input, IEnumerable<int?> expectedValues)
+        {
+            Service.Instance.ValueRetrievers.Register(new NullValueRetriever("<null>"));
+            var table = new Table("Field", "Value");
+            table.AddRow("MyExampleValues", input);
+
+            var expected = expectedValues.ToList();
+
+            var test = table.CreateInstance<Example>();
+            test.MyExampleValues.Should().BeEquivalentTo(expected);
+
+
+        }
+    }
+}