Affects Version/s: Master
When editing a Web Content Stucture's JSON in the Source tab, if you delete everything or delete the fields element, errors are thrown.
Steps to Reproduce
1. Go to Site Content -> Web Content -> (kebab) -> Structures
2. Add a structure
3. Add an element to the Structure in the View tab (ex. a Date)
4. Go over to the Source Tab and delete all contents of it.
5. Go back to the View Tab.
Expected Result: No errors are thrown in the browser's console
Actual Result: An error is thrown, Uncaught SyntaxError: Unexpected end of JSON input.
6. Refresh the page and return to the Source tab
7. Delete the Fields element (only availableLanguageId and defaultLanguageId should be left).
Expected Result: No errors are thrown in the console
Actual Result: Uncaught TypeError: Cannot read property 'forEach' of undefined is thrown in the console.