fix null casting for simple list

Dapper/SqlMapper.cs

@@ -383,7 +383,16 @@ private static IDataReader GetReader(IDbConnection cnn, IDbTransaction tranactio
         private static object GetStructDeserializer<T>(IDataReader reader)
         {
             Func<IDataReader, T> deserializer = null;
-            deserializer = r => (T)r.GetValue(0);
+
+            deserializer = r =>
+            {
+                var val = reader.GetValue(0);
+                if (val == DBNull.Value)
+                {
+                    val = null;
+                }
+                return (T)val;
+            };
             return deserializer;
         }
 

Tests/Tests.cs

@@ -121,6 +121,10 @@ public void TestStrongType()
                 .IsEqualTo(guid);
         }
 
+        public void TestSimpleNull()
+        {
+            connection.ExecuteMapperQuery<DateTime?>("select null").First().IsNull();
+        }
 
         public void TestExpando()
         {