Preset multiselects with null default value prevents any selection

[malcolmh]

What steps will reproduce the problem?

1. Add default="" to a multiselect header
2. Select suitable object in map
3. Invoke the preset

What is the expected result?

No selection, but usual multiple selections possible as if there were no default in the header

What happens instead?

All values are greyed out, no selection possible

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

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-01-06 17:30:31 +0100 (Wed, 06 Jan 2016)
Build-Date:2016-01-06 16:32:31
Revision:9329
Relative:URL: ^/trunk

Identification: JOSM/1.5 (9329 en) Mac OS X 10.11.2
Memory Usage: 493 MB / 910 MB (345 MB allocated, but free)
Java version: 1.8.0_66, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
VM arguments: [-Djava.library.path=/Applications/JOSM.app/Contents/MacOS, -DLibraryDirectory=/Users/mherring/Library, -DDocumentsDirectory=/Users/mherring/Documents, -DApplicationSupportDirectory=/Users/mherring/Library/Application Support, -DCachesDirectory=/Users/mherring/Library/Caches, -DSandboxEnabled=false, -Dapple.laf.useScreenMenuBar=true, -Dcom.apple.macos.use-file-dialog-packages=true, -Dcom.apple.macos.useScreenMenuBar=true, -Dcom.apple.mrj.application.apple.menu.about.name=JOSM, -Dcom.apple.smallTabs=true]

Plugins:
- SeaChart (31955)
- SeaMapEditor (31772)
- apache-commons (31895)
- dataimport (31772)
- ejml (31895)
- geotools (31895)
- imagery_offset_db (31895)
- imageryadjust (31772)
- jts (31772)
- opendata (31937)
- print (31895)
- reverter (31897)
- undelete (31895)
- utilsplugin2 (31895)

[simon04]

This relates to ​https://github.com/OpenNauticalChart/josm/issues/1 – sorry, I track you ;-)

1. Defining default="" is superfluous since it is the default
2. When you specify default="", an item with value "" must be present – test w/ the preset attached to #12160