The "first column as null gives null object" is by-design;

tweak tests to represent this (and workaround)

Added [ActiveTest] to allow trivial debugging individual tests

Dapper/SqlMapper.cs

@@ -16,6 +16,7 @@
 using System.Text;
 using System.Threading;
 using System.Text.RegularExpressions;
+using System.Diagnostics;
 
 namespace Dapper
 {
@@ -1622,8 +1623,8 @@ static List<FieldInfo> GetSettableFields(Type t)
 #endif
 )
         {
+            
             var dm = new DynamicMethod(string.Format("Deserialize{0}", Guid.NewGuid()), typeof(object), new[] { typeof(IDataReader) }, true);
-
             var il = dm.GetILGenerator();
             il.DeclareLocal(typeof(int));
             il.DeclareLocal(type);

Tests/Program.cs

 using System;
 using System.Data.SqlClient;
 using System.Reflection;
-
+using System.Linq;
 namespace SqlMapper
 {
     [ServiceStack.DataAnnotations.Alias("Posts")]
@@ -112,7 +112,10 @@ private static void RunTests()
         {
             var tester = new Tests();
             int fail = 0;
-            foreach (var method in typeof(Tests).GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly))
+            MethodInfo[] methods = typeof(Tests).GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly);
+            var activeTests = methods.Where(m => Attribute.IsDefined(m, typeof(ActiveTestAttribute))).ToArray();
+            if (activeTests.Length != 0) methods = activeTests;
+            foreach (var method in methods)
             {
                 Console.Write("Running " + method.Name);
                 try
@@ -136,4 +139,8 @@ private static void RunTests()
             }
         }
     }
+
+    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
+    public sealed class ActiveTestAttribute : Attribute {}
+
 }

Tests/Tests.cs

@@ -798,6 +798,19 @@ class Category
             // assertions
             product.Id.IsEqualTo(1);
             product.Name.IsEqualTo("abc");
+            product.Category.IsNull();
+        }
+        public void TestMultiMapWithSplitWithNullValueAndSpoofColumn() // http://stackoverflow.com/q/10744728/449906
+        {
+            var sql = @"select 1 as id, 'abc' as name, 1 as spoof, NULL as description, 'def' as name";
+            var product = connection.Query<Product, Category, Product>(sql, (prod, cat) =>
+            {
+                prod.Category = cat;
+                return prod;
+            }, splitOn: "spoof").First();
+            // assertions
+            product.Id.IsEqualTo(1);
+            product.Name.IsEqualTo("abc");
             product.Category.IsNotNull();
             product.Category.Id.IsEqualTo(0);
             product.Category.Name.IsEqualTo("def");