Fix the error produced by Form Element Helper in Sentry

[anantais]

This is a ticket for fixing for one of the errors that have been repeating in the cms-notifications channel in Slack. You will need to investigate this error and fix the issue in the code that is causing it.

Error Message from Sentry below:

TypeError: implode(): Argument #1 ($array) must be of type array, string given in implode() (line 26 of /var/www/cms/docroot/core/lib/Drupal/Core/Form/FormElementHelper.php). [dd.trace_id=9223372036854775807 dd.span_id=627650737601576824]

Culprit:
/modules/contrib/monolog/src/Logger/Handler/DrupalHandler.php in Drupal\monolog\Logger\Handler\DrupalHandler::write

View in Sentry:
http://sentry.vfs.va.gov/organizations/vsp/issues/250077/?referrer=webhooks_plugin

Notes: This same error sometimes occurs daily but can show up multiple times per week.

Acceptance Criteria

• Error is no longer present in the cms-notifications.