title: How do you check if a field is empty in drupal 8?
body: <p>I have a field added to the content type of basic page. It is a select box, which is either checked or unchecked depending on whether or not the page is of the 'getting started' kind. I want to add the class 'getting-started' to the body element in the html if the page is a getting started page, i.e. the box is checked. I want to do this in the .theme file. So essentially I want to check too see if the field is empty, and if it isn't add the class to the body element. Any help would be much appreciated.</p>