X++ Write file with hex code NULL

Hello,

I want to create a gif-file. I get hex-code from a webservice which I need to convert to a file.
The response from the webservice is for example "474946383961de00de00f00" which I need to write to a .gif file.
When I try the following example, it doesn't return the "00", so when I open the file in an hexeditor I still get "474946383961dedef0".
How can I do that?

static void Job00001(Args _args)
{
    AsciiIO     asciiFile;
    int         i;
    #file
    container   c;
    ;
    c += "47";
    c += "49";
    c += "46";
    c += "38";
    c += "39";
    c += "61";
    c += "de";
    c += "00";
    c += "de";
    c += "00";
    c += "f0";
    c += "00";
    c += "00";
    c += "00";
    c += "00";
    c += "00";
    c += "00";
    c += "ff";
    c += "ff";
    c += "ff";
    c += "2c";
    asciiFile = new asciiIo(@"C:\temp\file.gif", #io_write);
    for (i=1; i<=conlen(c); i+=1)
    {
        asciiFile.writeChar(hex2int(conpeek(c, i)));
    }
    info("END");
}