Remove unnecessary reflection call

This is the only call to TypeExtensions.IsValueType, so we can remove
that method, making the whole type conditionally compiled out for .NET 3.5

1 files changed, 2 insertions, 1 deletions

diff --git a/csharp/src/Google.Protobuf/FieldCodec.cs b/csharp/src/Google.Protobuf/FieldCodec.cs
index 98313088..c28b47e1 100644
--- a/csharp/src/Google.Protobuf/FieldCodec.cs
+++ b/csharp/src/Google.Protobuf/FieldCodec.cs
@@ -347,7 +347,8 @@ namespace Google.Protobuf
     public sealed class FieldCodec<T>
     {
         private static readonly T DefaultDefault;
-        private static readonly bool TypeSupportsPacking = typeof(T).IsValueType() && Nullable.GetUnderlyingType(typeof(T)) == null;
+        // Only non-nullable value types support packing. This is the simplest way of detecting that.
+        private static readonly bool TypeSupportsPacking = default(T) != null;
 
         static FieldCodec()
         {