Bug#907933: arctica-greeter FTBFS with vala 0.42.0-1

[Adrian Bunk]

Source: arctica-greeter
Version: 0.99.1.0-2
Severity: serious
Tags: ftbfs

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/arctica-greeter.html

...
gcc -DHAVE_CONFIG_H -I. -I..   -Wdate-time -D_FORTIFY_SOURCE=2 -pthread -D_REENTRANT -I/usr/include/gtk-3.0 -I/usr/include/libayatana-ido3-0.4 -I/usr/include/libayatana-indicator3-0.4 -I/usr/include/gtk-3.0 -I/usr/include/at-spi2-atk/2.0 -I/usr/include/at-spi-2.0 -I/usr/include/dbus-1.0 -I/usr/lib/x86_64-linux-gnu/dbus-1.0/include -I/usr/include/gtk-3.0 -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0 -I/usr/include/fribidi -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -I/usr/include/lightdm-gobject-1 -I/usr/include/gio-unix-2.0/ -I/usr/include/libxml2 -I/usr/include/cairo -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/uuid -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/pixman-1 -w -DGETTEXT_PACKAGE=\"arctica-greeter\" -DLOCALEDIR=\""/usr/share/locale"\" -DVERSION=\"0.99.1.0\" -DPKGDATADIR=\""/usr/share/arctica-greeter"\" -DPKGLIBEXECDIR=\""/usr/lib/x86_64-linux-gnu/arctica-greeter"\" -DINDICATORDIR=\""/usr/lib/ayatana-indicators3/7/"\" -g -O2 -ffile-prefix-map=/build/1st/arctica-greeter-0.99.1.0=. -fstack-protector-strong -Wformat -Werror=format-security -c -o logo_generator-logo-generator.o `test -f 'logo-generator.c' || echo './'`logo-generator.c
background.vala:447.5-447.37: error: Property `Background.current_background' with custom `get' accessor and/or `set' mutator cannot have `default' value
    public string? current_background {
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^