code: function toInclude(value) {
    if (Array.isArray(value)) {
      return {
        type:    'list',
        columns: value
      }
    }
    else if (typeof value === 'string' && (value === 'all' || value === 'none')) {
      return {
        type: value
      }
    }
    else if (utils.isObject(value)) {
      return value
    }
    else {
      throw new FieldError('Unknown toInclude value: ' + value)
    }
  }
docs: Set toInclude field
  
  @see http://druid.io/docs/0.6.121/SegmentMetadataQuery.html
  @param {string|string[]} value
  @returns {object}