WSOD when creating a webform page

Problem/Motivation

After attaching a webform entity to a Webform page, I get WSOD with the following error:

TypeError: civictheme_get_field_theme_value(): Argument #1 ($entity) must be of type Drupal\Core\Entity\FieldableEntityInterface, null given, called in /app/web/themes/custom/civictheme/includes/form.inc on line 89 in civictheme_get_field_theme_value() (line 450 of themes/custom/civictheme/includes/utilities.inc).

Steps to reproduce

1. Create a webform

2. Create a webform page

3. Attach webform from step 1 to the webform page and Save.

using CivicTheme 1.5.1

Temporary dirty workaround (for now): comment line 20 in civictheme/includes/form.inc