Can't remove the content of a macro once added

XWiki version: 9.8.1

Steps to reproduce:

• Create a simple wiki macro with the 'Macro content type' option set to 'Optional'
• Edit a page in wysiwyg and insert the macro created above
• Edit the macro and add some text to its content and click on send button
• Edit the macro again, remove the text of the content field and click on send button
• Edit the macro again and observe the content field

Expected result: The content field of the macro is empty.
Current result: The content field of the macro contains the removed text.