bgp announce default route to lower router, what is the bird version of default-originate / default-information orginate?

How can I announce a default route to a lower router who does not need a full table. What is de Bird equivalent of "default-orginitate" or "default-information originate". Currently I use a filter with a static blackhole route: protocol static { route 0.0.0.0/0 blackhole; } filter senddefault { if net = 0.0.0.0/0 then accept; reject; } template bgp local_as_ibgp_lowrouter { # export filter senddefault; }