fix regression with Guid mapping

Dapper/SqlMapper.cs

@@ -926,11 +926,7 @@ private static CacheInfo GetCacheInfo(Identity identity)
             }
 #endif
 
-            if (
-                (type.IsClass && type != typeof(string) && type != typeof(byte[]) && type != typeof(System.Data.Linq.Binary)) ||
-                (type.IsValueType && !type.IsPrimitive && !(type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>))
-                && type != typeof(Guid))
-                )
+            if (!typeMap.ContainsKey(type))
             {
                 return GetTypeDeserializer(type, reader, startBound, length, returnNullIfFirstMissing);
             }

Tests/Tests.cs

@@ -16,6 +16,24 @@ class Tests
     {
         SqlConnection connection = Program.GetOpenConnection();
 
+
+        public void TestNullableGuidSupport()
+        {
+            var guid = connection.Query<Guid?>("select null").First();
+            guid.IsNull();
+
+            guid = Guid.NewGuid();
+            var guid2 = connection.Query<Guid?>("select @guid", new { guid }).First();
+            guid.IsEqualTo(guid2);
+        }
+
+        public void TestNonNullableGuidSupport()
+        {
+            var guid = Guid.NewGuid();
+            var guid2 = connection.Query<Guid?>("select @guid", new { guid }).First();
+            Assert.IsTrue(guid == guid2);
+        }
+
         struct Car
         {
             public enum TrapEnum : int