Crash on Destructor of QSystemTrayIcon

Crash on Destructor of QSystemTrayIcon:

Stack trace:
0 XFreeColormap /usr/lib/i386-linux-gnu/libX11.so.6 0 0x17a7d52
1 QSystemTrayIconSys::~QSystemTrayIconSys qsystemtrayicon_x11.cpp 213 0xa87d86
2 QSystemTrayIconSys::~QSystemTrayIconSys qsystemtrayicon_x11.cpp 214 0xa87e15
3 QSystemTrayIconPrivate::remove_sys qsystemtrayicon_x11.cpp 354 0xa888d1
4 QSystemTrayIcon::~QSystemTrayIcon qsystemtrayicon.cpp 152 0xa733d6
5 QSystemTrayIcon::~QSystemTrayIcon qsystemtrayicon.cpp 153 0xa73435
6 BackupService::~BackupService backupservice.cpp 16 0x804fcbc
7 main main.cpp 10 0x804fa4e

The line signed (->) above is the problem,
if (colormap)
-> XFreeColormap(display, colormap);

the display var is NULL

I think if code are changed to
if (display && colormap)
XFreeColormap(display, colormap);

The bug will be solved.

that bug are associated with this:
https://bugs.launchpad.net/ubuntu/+source/hplip/+bug/505460