In case of RichText XML validation fails, fatal error displayed:

Argument 2 passed to Symfony\Component\Validator\Util\PropertyPath::append() must be of the type string, null given, called in /app/vendor/ezsystems/ezplatform-content-forms/src/lib/Validator/Constraints/FieldValueValidator.php on line 92 [in vendor/symfony/validator/Util/PropertyPath.php:34]

The simplest way to reproduce it with custom tags:

STR

• Create new custom tag with 2 attributes:

  test:
              template: '@ezdesign/custom_tag/test.html.twig'
              icon: '/assets/build/shared/images/custom-tag-icons.svg#test'
              is_inline: false
              attributes:
                  test_one:
                      type: string
                      default_value: ''
                      required: false
                  test_two:
                      type: string
                      default_value: ''
                      required: false
  

• Edit any content with richtext and add custom tag with both attributes filled.
• Publish content
• remove custom tag attribute:

  test:
              template: '@ezdesign/custom_tag/test.html.twig'
              icon: '/assets/build/shared/images/custom-tag-icons.svg#test'
              is_inline: false
              attributes:
                  test_one:
                      type: string
                      default_value: ''
                      required: false
  

• Edit same content object, but didn't change richtext field
• Click Publish

Actual Result
Fatal Error displayed

Expected Result
Error message displayed near RichText field:

Validation of XML content failed: Unknown attribute 'test_two' of RichText Custom Tag 'test'

PRs:
https://github.com/ezsystems/ezplatform-content-forms/pull/34
https://github.com/ezsystems/ezplatform-richtext/pull/164