Cannot delete files from draft submission with radios element required

Steps to reproduce:

1. Create a webform with draft feature activated
2. Create a radios element with 2 options and setup as required
4. Create a document file element
5. Visit the form and upload a file
6. Save it as a draft
7. Try to remove file (see webform_error.png attached)

This is source (YAML), also an entire configuration is provided

radios_test:
  '#type': radios
  '#title': 'Radios test'
  '#options':
    10: '10'
    20: '20'
  '#required': true
document_test:
  '#type': document_file
  '#title': 'Document Test'