Steps

• Install ibexa
• add a block with richtext https://doc.ibexa.co/en/4.5/content_management/rich_text/create_custom_richtext_block/
• make the richtext field required, add validator not_blank_richtext
• Create a landing page
• add newly created block (do not add any content in the block)
• save draft

Result
PB breaks, blank page visible. An exception is thrown DOMDocument::loadXML(): Argument #1 ($source) must not be empty, stack trace attached.

Expected result
Draft saves, PB still works.