Mongoose multiple validations

Express error handling.js

var sys = require ('sys');

module.exports = function(app) {

    function NotFound(msg) {
      this.name = 'NotFound';
      Error.call(this, msg);
      Error.captureStackTrace(this, arguments.callee);
    }

    sys.inherits(NotFound, Error);

    app.get("*", function(req, res, next){
      res.render('500.jade', { status: 500, error: err });
    });

    app.error(function(err, req, res, next){
      if (err instanceof NotFound) {
        res.render('404.jade', { status: 404, error: err });
      } else {
        next(err);
      }
    });

    app.error(function(err, req, res) {
      res.render('500.jade', { status: 500, error: err });
    });

}

Express, mongoose error

GET /posts/new 9 ms
POST /posts/ 5 ms
ValidatorError: Validator "content can't be empty" failed for path content
    at validate (/usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/schematype.js:221:10)
    at /usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/schematype.js:237:9
    at Array.forEach (native)
    at SchemaString.doValidate (/usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/schematype.js:226:19)
    at Array.1 (/usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/document.js:380:30)
    at EventEmitter._tickCallback (node.js:108:26)

node.js:116
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: Can't set headers after they are sent.
    at ServerResponse.<anonymous> (http.js:504:11)
    at ServerResponse.setHeader (/usr/local/lib/node/.npm/connect/1.0.3/package/lib/patch.js:39:15)
    at next (/usr/local/lib/node/.npm/connect/1.0.3/package/lib/http.js:168:13)
    at /usr/local/lib/node/.npm/connect/1.0.3/package/lib/middleware/router.js:151:19
    at model.<anonymous> (/home/korsaks/projects/own/routes/posts.js:47:29)
    at error (/usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/document.js:576:21)
    at parallel (/usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/document.js:596:20)
    at /usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/document.js:383:18
    at validate (/usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/schematype.js:221:7)
    at /usr/local/lib/node/.npm/mongoose/1.1.3/package/lib/mongoose/schematype.js:237:9

Mongoose save method.js

app.post('/posts/', function(req, res, next){
        var post = new Post(req.body.post);
        post.save(function(err) {
            if (err) return next(err);
            req.flash("info", "Successfully create post _%s_", post.title);
            res.redirect('/posts/' + post.id);
        });
});