build query string

function buildQuery(params) {
  if (!isPlainObject(params)) {
    return null;
  }
  function build(data, name) {
    var result = [];
    for (var key in data) {
      if (data.hasOwnProperty(key)) {
        var value = data[key];
        key = encodeURIComponent(key);
        if (name) {
          key = name + '[' + key + ']';
        }
        if (isPlainObject(value) || isArray(value)) {
          result.push(arguments.callee(value, key));
        } else {
          result.push(key + '=' + encodeURIComponent(value));
        }
      }
    }
   return result.join('&');
  }
  return build(params);
}