SyntaxWarning in dhcp_host_domain while booting HBD

I plugged UART cable to the Turris Omnia router which has HBD branch and I noticed this warning while it was booting:

[    9.785704] device lan4 entered promiscuous mode
[    9.826746] mv88e6085 f1072004.mdio-mii:10: p5: already a member of VLAN 1
[    9.854006] mvneta f1034000.ethernet eth2: PHY [f1072004.mdio-mii:01] driver [Marvell 88E1510] (irq=POLL)
[    9.863860] mvneta f1034000.ethernet eth2: configuring for phy/sgmii link mode
[    9.930339] mv88e6085 f1072004.mdio-mii:10 lan3: Link is Up - 1Gbps/Full - flow control rx/tx
[    9.940642] br-lan: port 4(lan3) entered blocking state
[    9.945917] br-lan: port 4(lan3) entered forwarding state
[    9.967543] IPv6: ADDRCONF(NETDEV_CHANGE): br-lan: link becomes ready
[   15.042215] mvneta f1034000.ethernet eth2: Link is Up - 1Gbps/Full - flow control rx/tx
[   15.050261] IPv6: ADDRCONF(NETDEV_CHANGE): eth2: link becomes ready
/etc/resolver/dhcp_host_domain_ng.py:50: SyntaxWarning: "is" with a literal. Did you mean "=="?
  if output is "syslog":