Notice: Undefined index: #datepicker_title in Drupal\bootstrap_datepicker\Element\BootstrapDate::processBootstrapDate

If user creates form item for datepicker manually and doesn't enter the #datepicker_title in the array, there occurs the undefined index warning. The patch in the attachment should fix this case. NULL is then displayed as an empty table row in the output which is better than PHP warning I guess. Thank you for possible fix in the upstream code.