What am I doing wrong?

using System;

class Binary
{
    public static string Bin(uint number)
    {


        if( number / 2 == 0)
        {
            Console.Write(number % 2);
        }

        else
        {
            Bin(number/2);
            Console.Write( number % 2 );
        }

        return null;


    }
    public static void Main( )
    {
        Console.WriteLine("Enter a decimal number: ");
        uint number = uint.Parse( Console.ReadLine() );

        string result = Bin ( number );

        Console.WriteLine(result.PadLeft(32,'0'));

    }
}