_g_dbus_method_invocation_new is said to allow method_info == NULL, but will crash inside g_dbus_method_info_ref when the method_info really is NULL, because g_dbus_method_info_ref does not allow NULL as parameter. Found while looking for a leak.

The leak itself happens because _g_dbus_method_invocation_new stores a new reference to the method_info without also unreferencing it. Found in SyncEvolution, which creates GDBusMethodInfo instances dynamically.

I'll attach a patch.

FWIW, the whole concept of reference counting for GDBusMethodInfo and GDBusSignalInfo is pretty pointless because in GDBusInterfaceInfo one has to store plain pointers in a class which does not support reference counting for these pointers.