Tagging presets: Setting default value in multiselect can disable the selection

[skyper]

What steps will reproduce the problem?

1. Have preset with a default value set for a <multiselect> with the optional default=""
2. Create a new object
3. Open preset and try to select values in the list.

What is the expected result?

The default value should be selected and selecting more value and deselecting the default value should be possible

What happens instead?

The value list is greyed out and no selection is possible, plus the default value is not selected.

Please provide any additional information below. Attach a screenshot if possible.

I also tried with tested (r18193) and there is no difference.
Without the optional default="" the multiselect works as expected, besides #21397.
This is similar to #21385 but rather the opposite as it works if a valid combination of values is already tagged.

from Presets/MastAndTower "Big communication tower" preset:

    <multiselect key="tower:type" text="Type of tower" values_searchable="true" values_sort="false" default="communication" rows="3">
        <list_entry value="communication" display_value="Communication tower" icon="presets/tower/communication.svg" />
        <list_entry value="observation" display_value="Observation tower" icon="presets/tower/observation.svg" />
    </multiselect>

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2021-10-04 16:05:23 +0200 (Mon, 04 Oct 2021)
Revision:18246
Build-Date:2021-10-04 14:06:33
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (18246 en) Linux Debian GNU/Linux 11 (bullseye)
Memory Usage: 247 MB / 256 MB (74 MB allocated, but free)
Java version: 17-ea+19-Debian-1, Debian, OpenJDK 64-Bit Server VM
Look and Feel: javax.swing.plaf.metal.MetalLookAndFeel
Environment variable LANG: en_US.utf8
System property file.encoding: UTF-8
System property sun.jnu.encoding: UTF-8
Locale info: en_US
Numbers with default locale: 1234567890 -> 1234567890
Desktop environment: GNOME
libcommons-compress-java: libcommons-compress-java:all-1.20-1
libcommons-logging-java: libcommons-logging-java:all-1.2-2
fonts-noto: fonts-noto:all-20201225-1
VM arguments: [-Djosm.home=<josm.pref>/]
Dataset consistency test: No problems found

Plugins:
+ flatlaf (35799)
+ tagging-preset-tester (35640)

[Don-vip]

In 18254/josm:

fix #21408 - fix #19013, fix #21385, fix #21404 - Fix MultiSelect issues (patch by marcello)

[skyper]

Thanks, this seems to work nicely, now.

[Don-vip]

Milestone renamed