When there is only one Section .. SectionEnd, this mandatory section isn't "selected" unless things go through one of the selection pages. It looks like this was lost in early 2018 when SectionGroup and SectionGroupEnd was added (I guess the focus then was on selection things, not having nothing to select from).
(When nothing is installed, no (new) directory is created, and very little can be written to this non-existing directory - not even the uninstaller).
The easiest workaround for now is to add an empty section ...
Section "Dummy"
SectionEnd
... or, of course, fill it with something more useful...