Manipulates the default behavior of Model Binding to initialize strings to String.Empty. (as in ASP.NET MVC 1.0)

EmptyStringModelBindingAspect.cs

using System;
using System.Linq;
using System.Reflection;
using MySolution;
using PostSharp.Aspects;
using PostSharp.Extensibility;

[assembly: EmptyStringModelBindingAspect(
    AttributeTargetTypes = @"regex:[^\.]*\.Controllers\..*Controller",
    AttributeTargetTypeAttributes = MulticastAttributes.Public,
    AttributeTargetElements = MulticastTargets.Method,
    AttributeTargetMemberAttributes = MulticastAttributes.Public)]

namespace MySolution
{
    [Serializable]
    public class EmptyStringModelBindingAspect : MethodInterceptionAspect
    {
        public override void OnInvoke(MethodInterceptionArgs args)
        {
            for (int i = 0; i < args.Arguments.Count; i++)
            {
                FixString(args, i);
                FixStringsInObjects(args.Arguments[i]);
            }
            args.Proceed();
        }

        private static void FixString(MethodInterceptionArgs args, int i)
        {
            if (args.Arguments[i] is string &&
                args.Arguments[i] == null)
            {
                args.Arguments.SetArgument(i, string.Empty);
            }
        }

        private static void FixStringsInObjects(object obj)
        {
            if (obj == null)
            {
                return;
            }

            Type type = obj.GetType();
            PropertyInfo[] properties = (from p in type.GetProperties()
                                         where p.PropertyType == typeof(string) &&
                                               p.CanRead &&
                                               p.CanWrite &&
                                               p.GetValue(obj, null) == null
                                         select p).ToArray();

            foreach (PropertyInfo item in properties)
            {
                item.SetValue(obj, string.Empty, null);
            }
        }

        public override bool CompileTimeValidate(MethodBase method)
        {
            return !(method.Name.StartsWith("get_") || method.Name.StartsWith("set_"));
        }
    }
}

how could you tell the type of an argument if its value is null? For me (using MVC 4) "if(args.Arguments[i] is string)" always returns false

I solved it like this:

   private static void FixString(MethodInterceptionArgs args, int i)
    {
        ParameterInfo[] paramInfo = args.Method.GetParameters();          
        if (paramInfo[i].ParameterType == typeof(string) && args.Arguments[i] == null)
            {
                args.Arguments.SetArgument(i, string.Empty);
            }
    }