blueman-manager crashed with TypeError in close_rfcomm(): a bytes-like object is required, not 'str'

Closing a modem port on a bluetooth-connected mobile phone.

ProblemType: Crash
DistroRelease: Ubuntu 17.10
Package: blueman 2.0.4-1ubuntu3
ProcVersionSignature: Ubuntu 4.12.0-11.12-lowlatency 4.12.5
Uname: Linux 4.12.0-11-lowlatency x86_64
ApportVersion: 2.20.7-0ubuntu1
Architecture: amd64
CrashCounter: 1
CurrentDesktop: XFCE
Date: Wed Aug 30 19:28:23 2017
ExecutablePath: /usr/bin/blueman-manager
InstallationDate: Installed on 2011-10-14 (2147 days ago)
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111011)
InterpreterPath: /usr/bin/python3.6
ProcCmdline: /usr/bin/python3 /usr/bin/blueman-manager
Python3Details: /usr/bin/python3.6, Python 3.6.2, python3-minimal, 3.6.1-0ubuntu3
PythonArgs: ['/usr/bin/blueman-manager']
PythonDetails: /usr/bin/python2.7, Python 2.7.13, python-minimal, 2.7.13-2
SourcePackage: blueman
Title: blueman-manager crashed with TypeError in close_rfcomm(): a bytes-like object is required, not 'str'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin audio cdrom dialout fax floppy lpadmin lxd plugdev pulse-access sambashare