function _addUserError(exception) {
  if (!this.isActive()) {
    logger.trace('Transaction is not active. Not capturing user error: ', exception)
    return
  }

  this._linkExceptionToSegment(exception)
  this.userErrors.push(exception)
}
Associate a user error (reported using the noticeError() API) with the transaction.
When the transaction ends, the exception will be collected along with the transaction
details.

@param {Exception}  exception  The exception object to be collected.