Cannot add conditional field or global field

Problem/Motivation

I am unable to add a Views Conditional Field or a Global custom text field to my view when using FullCalendar as the Format.

Steps to reproduce

When I add a Views Conditional Field OR a global custom text field, it gives me an error. I can save the View but when I access the view, it gives the following error:

TypeError: fullcalendar_field_is_date(): Argument #1 ($field) must be of type Drupal\views\Plugin\views\field\EntityField, Drupal\views\Plugin\views\field\Custom given, called in /public_html/modules/contrib/fullcalendar/src/Plugin/views/style/FullCalendar.php on line 390 in fullcalendar_field_is_date() (line 79 of modules/contrib/fullcalendar/fullcalendar.module).

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes