libvirt virNetworkGetDHCPLeases error on 18.03

[nh2]

With up upgrade to nixpkgs release-18.03, I started seeing this in about 50% of my libvirt nixops deployments:

node-3..> uploading key ‘mykey’...
libvirt: Network Driver error : invalid network pointer in virNetworkGetDHCPLeases
node-1..> error: Traceback (most recent call last):
  File "/nix/store/p80ilh2vvk82h4cvysca3s31v2ak2rms-python2.7-nixops-1.6pre0_abcdef/lib/python2.7/site-packages/nixops/deployment.py", line 715, in worker
    m.send_keys()
  File "/nix/store/p80ilh2vvk82h4cvysca3s31v2ak2rms-python2.7-nixops-1.6pre0_abcdef/lib/python2.7/site-packages/nixops/backends/__init__.py", line 281, in send_keys
    self.upload_file(tmp, tmp_outfile)
  File "/nix/store/p80ilh2vvk82h4cvysca3s31v2ak2rms-python2.7-nixops-1.6pre0_abcdef/lib/python2.7/site-packages/nixops/backends/__init__.py", line 431, in upload_file
    cmdline += [source, "root@" + self.get_ssh_name() + ":" + target]
  File "/nix/store/p80ilh2vvk82h4cvysca3s31v2ak2rms-python2.7-nixops-1.6pre0_abcdef/lib/python2.7/site-packages/nixops/backends/libvirtd.py", line 267, in get_ssh_name
    self.private_ipv4 = self._parse_ip()
  File "/nix/store/p80ilh2vvk82h4cvysca3s31v2ak2rms-python2.7-nixops-1.6pre0_abcdef/lib/python2.7/site-packages/nixops/backends/libvirtd.py", line 226, in _parse_ip
    ifaces = self.dom.interfaceAddresses(libvirt.VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_LEASE, 0)
  File "/nix/store/jzjp87fbh4k2kdf5vky3gyddipq6d74f-python2.7-libvirt-3.10.0/lib/python2.7/site-packages/libvirt.py", line 1347, in interfaceAddresses
    if ret is None: raise libvirtError ('virDomainInterfaceAddresses() failed', dom=self)
libvirtError: invalid network pointer in virNetworkGetDHCPLeases

Not sure what that is; googling invalid network pointer in virNetworkGetDHCPLeases yields 0 results.