gnome-power-manager crashes due to an unhandled X error on systems without XBACKLIGHT:

Gdk-ERROR **: The program 'gnome-power-manager' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadAtom (invalid Atom parameter)'.
  (Details: serial 160 error_code 5 request_code 150 minor_code 15)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
aborting...
Trace/breakpoint trap (core dumped)

+ Trace 223360

        session = 0x6c0b70
        manager = <value optimized out>
        error = 0x0
        context = 0x637320
        ret = <value optimized out>
        options = {{long_name = 0x4214e0 "verbose", short_name = 0 '\000', flags = 0, arg = G_OPTION_ARG_NONE, arg_data = 0x7fffffffe16c, description = 0x421648 "Show extra debugging information", arg_description = 0x0}, {long_name = 0x4214e8 "version", short_name = 0 '\000', flags = 0, arg = G_OPTION_ARG_NONE, 
            arg_data = 0x7fffffffe168, description = 0x421670 "Show version of installed program and exit", arg_description = 0x0}, {long_name = 0x4214f0 "timed-exit", short_name = 0 '\000', flags = 0, arg = G_OPTION_ARG_NONE, arg_data = 0x7fffffffe164, 
            description = 0x4216a0 "Exit after a small delay (for debugging)", arg_description = 0x0}, {long_name = 0x4214fb "immediate-exit", short_name = 0 '\000', flags = 0, arg = G_OPTION_ARG_NONE, arg_data = 0x7fffffffe160, description = 0x4216d0 "Exit after the manager has loaded (for debugging)", 
            arg_description = 0x0}, {long_name = 0x0, short_name = 0 '\000', flags = 0, arg = G_OPTION_ARG_NONE, arg_data = 0x0, description = 0x0, arg_description = 0x0}}
        __FUNCTION__ = "main"

This happens on 2.31.90. It looks like the same bug affects master too