Pass a{sv} parameters

[pothos]

Hello,
invoking with '{}' as parameter for type a{sv} works in mdbus but fails in mdbus2 (Debian package 2.3.3-2):

(mdbus2:6928): GLib-CRITICAL **: g_variant_builder_end: assertion '!GVSB(builder)->uniform_item_types || GVSB(builder)->prev_item_type != NULL || g_variant_type_is_definite (GVSB(builder)->type)' failed

(mdbus2:6928): GLib-CRITICAL **: g_variant_ref_sink: assertion 'value != NULL' failed

*SEGV*