If libsane-hpaio is installed and dbus isn't running, scanimage crashes:

   $ scanimage -L
   dbus[5852]: arguments to dbus_connection_send() were incorrect, assertion "connection != NULL" failed in file ../../../dbus/dbus-connection.c line 3307.
   This is normally a bug in some application using the D-Bus library.

     D-Bus not built with -rdynamic so unable to print a backtrace
   Aborted

Backtrace:

#0  0xf7f37559 in __kernel_vsyscall ()
#1  0xf7c69f36 in __libc_signal_restore_set (set=0xfff3d73c) at ../sysdeps/unix/sysv/linux/internal-signals.h:104
#2  __GI_raise (sig=<optimized out>) at ../sysdeps/unix/sysv/linux/raise.c:47
#3  0xf7c52312 in __GI_abort () at abort.c:79
#4  0xf4115d71 in _dbus_abort () at ../../../dbus/dbus-sysdeps.c:93
#5  0xf413ac5c in _dbus_warn_check_failed (format=0xf414c8f0 "arguments to %s() were incorrect, assertion \"%s\" failed in file %s line %d.\nThis is normally a bug in some application using the D-Bus library.\n") at ../../../dbus/dbus-internals.c:281
#6  0xf413b42b in _dbus_warn_return_if_fail (function=0xf4148bc0 <__func__.46> "dbus_connection_send", assertion=0xf4147852 "connection != NULL", file=0xf4147ab4 "../../../dbus/dbus-connection.c", line=3307) at ../../../dbus/dbus-internals.c:936
#7  0xf411ea6f in dbus_connection_send (connection=0x0, message=0x579be5d0, serial=0x0) at ../../../dbus/dbus-connection.c:3308
#8  0xf1a64476 in SendScanEvent (device_uri=<optimized out>, event=<optimized out>) at scan/sane/io.c:95
#9  0xf1a603b7 in DevDiscovery (localOnly=localOnly@entry=0) at scan/sane/hpaio.c:339
#10 0xf1a60698 in sane_hpaio_get_devices (deviceList=0xfff41c38, localOnly=0) at scan/sane/hpaio.c:379
#11 0xf7ef6e4b in sane_dll_get_devices (device_list=0xfff41da0, local_only=0) at dll.c:1098
#12 0xf7ef39dc in sane_get_devices (dl=0xfff41da0, local=0) at dll-s.c:21
#13 0x565866ff in main (argc=2, argv=0xfff440c4) at scanimage.c:2184