Trying to get escodegen's source-map generation to work

source-maps.js

var esprima   = require("esprima"),
    esmangle  = require("esmangle"),
    escodegen = require("escodegen"),
    
    src = "var fooga = \"wooga\";\n\nconsole.log(fooga);\n\nfooga += 1;",
    ast, result;

ast = esprima.parse(src, {
    loc    : true,
    tokens : true,
});
ast = esmangle.optimize(ast, null);
ast = esmangle.mangle(ast, null, {
    destructive : true
});

result = escodegen.generate(ast, {
    sourceMap         : "test",
    sourceMapWithCode : true,
    format    : {
        renumber    : true,
        hexadecimal : true,
        escapeless  : true,
        compact     : true,
        semicolons  : false,
        parentheses : false
    }
});

console.log(JSON.parse(result.map.toString()));

// OUTPUT
/*
C:\Users\pcavit\Documents\GitHub\node-web-build>node source-map.js
{ version: 3,
  file: 'test',
  sources: [ 'test' ],
  names: [],
  mappings: 'AAAA,GAAA,CAAI,MAAQ,OAAZ,CAEA,OAAA,IAAA,CAAY,KAAZ,C,CAEA,KAAA,EAAS' }
*/
// Where's the names?

Also attempted in a browser here: http://jsbin.com/omakoh/2/edit