Heimdal kerberos ipropd-master failing on start-up with "open (null): Bad address" error

I am trying to set up a Heimdal KDC environment with one master and one replica. When I try to start the replication service on the master, it fails with this error:

ipropd-master[22640]: open (null): Bad address

The command I am running is this:

/usr/sbin/ipropd-master -c /etc/heimdal-kdc/kdc.conf -k /etc/heimdal-kdc/iprop.keytab

Here is part of an strace I ran on the command:

open("/etc/heimdal-kdc/kdc.conf", O_RDONLY) = 3
read(3, "# Heimdal KDC configuration.  -*"..., 4096) = 4096
...
open("/var/run/ipropd-master.pid", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
write(3, "23677", 5)                    = 5
close(3)                                = 0
connect(3, {sa_family=AF_FILE, path="/dev/log"}, 110) = 0
...
open("/var/lib/heimdal-kdc/m-key", O_RDONLY|O_CLOEXEC) = 4
read(5, "\5", 1)                        = 1
read(5, "\2", 1)                        = 1
close(5)                                = 0
close(4)                                = 0
open(NULL, O_RDONLY)                    = -1 EFAULT (Bad address)
open("/etc/localtime", O_RDONLY)        = 5

It appears that ipropd-master is trying to open something but the argument to the open system call is NULL. This is happening right after ipropd-master has read the file /var/lib/heimdal-kdc/m-key.

I cannot figure out what ipropd-master is trying to open and failing to do so. I would appreciate any suggestions.