code: function toNested(map) {
  
    var split, first, last;
    utils.walkObject(map, function (val, prop1) {
  
      split = prop1.split('.');
  
      if (!utils.validateFieldName(prop1)) {
        log.error('map field name "' + prop1 + '" is invalid');
      }
  
      last = split[split.length - 1];
      first = prop1.replace('.' + last, '');
  
      utils.walkObject(map, function (val2, prop2) {
        if (prop1 !== prop2 && first === prop2) {
          log.error('map field name "' + prop2 + '" is invalid');
        }
      });
    });
  
    var form = {};
    var names = [];
  
    utils.walkObject(map, function (val, prop) {
      names.push({ keys: prop.split('.'), value: val });
    });
  
    var obj;
    names.forEach(function (name) {
      obj = form;
      name.keys.forEach(function (key, index) {
        if (index === name.keys.length - 1) {
          obj[key] = name.value;
        } else {
          if (!obj[key]) {
            obj[key] = {};
          }
          obj = obj[key];
        }
      });
    });
  
    return form;
  }
docs: Plain to nested.