make function optional without messing up 'n-ary' properties
make function optional without messing up 'n-ary' properties

amcat/amcat,tschmorleiz/amcat,amcat/amcat,amcat/amcat,tschmorleiz/amcat,amcat/amcat,amcat/amcat,tschmorleiz/amcat,tschmorleiz/amcat,tschmorleiz/amcat,amcat/amcat