ReturnAnEmptyCollection.cs

public void OnInvoke(MethodInterceptionArgs args)
{
    try
    {
      args.Proceed();
    }
    catch (Exception ex)
    {
      // ... snip ...
      ErrorReturn(args);
    }
}

void ErrorReturn(MethodInterceptionArgs args)
{
    try
    {
        var methodInfo = args.Method as MethodInfo;
        if (methodInfo == null)     // cast failed, so just give up
            return;
        else if (typeof(IEnumerable).IsAssignableFrom(methodInfo.ReturnType))
            args.ReturnValue = Activator.CreateInstance(methodInfo.ReturnType);
    }
    catch
    {
        // don't want any errors to take place trying to build the correct return value
        // so just swallow them, and let args.ReturnValue stay whatever it is
    }
}