topology.all_predecessors()

I am a little confused by the documentation for topology.all_predecessors (v.2.29)

https://graph-tool.skewed.de/static/doc/topology.html#graph_tool.topology.all_predecessors

The Parameters section says that pred_map is optional

pred_mapVertexPropertyMap (optional, default: None)

However the title line in the documentation suggests that pred_map must be supplied:

graph_tool.topology.all_predecessors(g, dist_map, pred_map, weights=None, epsilon=1e-08)

And running the code without supplying pred_map throws an error.

from graph_tool import generation as gt_generation
from graph_tool import topology as gt_topology
g = gt_generation.price_network(500)
distance_map = gt_topology.shortest_distance(g)
all_pred_map = gt_topology.all_predecessors(g, distance_map)

TypeError: all_predecessors() missing 1 required positional argument: 'pred_map'

So my follow-up question is: how do I generate a pred_map to supply to all_predecessors()?

I am running 2.29 on Python 3.6.7 packaged by conda-forge, MacOS 10.15.2

Thanks

Jonathan