apport-retrace crashed with AttributeError in join(): 'NoneType' object has no attribute 'endswith'

[Kamil]

When I wanted to use apport command line tools crash happened.

ProblemType: Crash
DistroRelease: Ubuntu 12.10
Package: apport-retrace 2.6.1-0ubuntu12
ProcVersionSignature: Ubuntu 3.5.0-37.58-generic 3.5.7.16
Uname: Linux 3.5.0-37-generic x86_64
ApportLog:
 ERROR: apport (pid 1741) Sat Jul 27 11:33:51 2013: called for pid 1724, signal 6, core limit 18446744073709551615
 ERROR: apport (pid 1741) Sat Jul 27 11:33:51 2013: ignoring implausibly big core limit, treating as unlimited
 ERROR: apport (pid 1741) Sat Jul 27 11:33:51 2013: executable: /usr/bin/Xorg (command line "/usr/bin/X :0 -core -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch")
 ERROR: apport (pid 1741) Sat Jul 27 11:33:51 2013: is_closing_session(): no DBUS_SESSION_BUS_ADDRESS in environment
 ERROR: apport (pid 1741) Sat Jul 27 11:33:51 2013: wrote report /var/crash/_usr_bin_Xorg.0.crash
ApportVersion: 2.6.1-0ubuntu12
Architecture: amd64
CrashReports:
 644:0:110:3858:2013-07-27 11:41:18.651635080 +0200:2013-07-27 11:40:49.007634310 +0200:/var/crash/_usr_bin_Xorg.0.backtrace.txt
 640:0:110:999536:2013-07-27 11:36:42.307627000 +0200:2013-07-27 11:37:12.871628707 +0200:/var/crash/_usr_bin_Xorg.0.crash
 640:0:110:13423:2013-07-27 11:44:57.595640000 +0200:2013-07-27 11:44:58.595640000 +0200:/var/crash/_usr_bin_apport-retrace.0.crash
Date: Sat Jul 27 11:44:58 2013
ExecutablePath: /usr/bin/apport-retrace
ExecutableTimestamp: 1372354520
InstallationDate: Installed on 2013-02-18 (158 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
InterpreterPath: /usr/bin/python2.7
MarkForUpload: True
PackageArchitecture: all
ProcCmdline: /usr/bin/python /usr/bin/apport-retrace /var/crash/_usr_bin_Xorg.0.crash -s
ProcCwd: /home/lukasz
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=pl_PL.UTF-8
 SHELL=/bin/bash
PythonArgs: ['/usr/bin/apport-retrace', '/var/crash/_usr_bin_Xorg.0.crash', '-s']
SourcePackage: apport
Title: apport-retrace crashed with AttributeError in join(): 'NoneType' object has no attribute 'endswith'
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: