Getting: 'Error: Not initialized' on line 15

gistfile1.js

var crypto = require('crypto');
var fs = require('fs');

var dir = fs.readdirSync('.');
for(var i=0; i<dir.length; ++i)
{
        var filename = dir[i];
        if(fs.statSync(filename).isFile()) {
                var md5 = crypto.createHash('md5');
                var s = fs.ReadStream(filename);
                s.on('data', function(data) {
                        md5.update(data);
                });
                s.on('end', function() {
                        console.log(md5.digest('hex'));
                });
        }
}

Full output:
89377bc3c57dfd486724018703295371

/home/zed0/test.js:15
console.log(md5.digest('hex'));
^
Error: Not initialized
at [object Object]. (/home/zed0/test.js:15:20)
at [object Object].emit (events.js:39:17)
at afterRead (fs.js:843:12)