Symmetry dialog is empty

Environment/Versions

• GIMP version: 2.99.13 (commit 47a56cf6)
• Package: Self-compiled
• Operating System: Kubuntu 20.04

Description of the bug

When Gimp starts, until an image is loaded the Symmetry dialog is totally empty, which is disconcerting and makes it appear non-functional (and not in line with other dialogs, that are at best disabled)

Reproduction

Reproduction steps:

1. Start Gimp (without an image argument)

…

Expected result: the symmetry dialog shows the Symmetry type drop-down, disabled

Actual result: the symmetry dialog is completely empty

Additional information

Same behavior in 2.10, but that doesn't make it less disconcerting. This possibly remained under the radar because the SP dialog is rarely the dialog that shows by default.