function buildExpandObject(expand) {
  if (!expand) {
    return {};
  }
  const fields = {};
  expand.split(',').forEach((prop) => {
    fields[prop] = true;
  });
  return fields;
}
@description Return an object of expanded fields.
@param {string} expand - The expand string.
@returns {object} The fields object.
@example
buildExpandObject('temperature,humidity');