Macro config UI empty when configuring macro with a unique optional parameter

Reproduction steps:

• Import the attached XAR which contains a page with a macro defined with a single optional parameter and no content
• Try to use that macro in a page e.g. by typing /mymacro in quick actions
• Double click on the inserted macro to open the macro configuration UI

Expected result:

• the macro config UI displays a unique parameter using a select as input

Obtained result:

• the macro config UI is empty: