Steps to reproduce

• npm run start:firefox
• Click "Import Blog Posts"
• Navigate to the screen where one clicks around to fill the blogpost
• Select the title of the post
• In your editor, rename the title field in ./schema/subjects/blog-post.json to something other than title. Note that it's fields.title we're modifying, not the top-level title.
• In your terminal, do npm run build:schema
• In your editor, add some blank lines in a TypeScript file and save it, so that the extension reloads
• The following error is displayed

Unexpected Application Error!
field is undefined

SingleFieldEditor@moz-extension://1c528d92-66fa-4917-afc2-4888dbede0f5/app.js:375190:1212