Tested on commit 9d3e3aa58dc4e76586b20a7b60c0495ae83a678f.

[straussd@systemd-f19 systemd]$ cat /etc/systemd/system/def@.service 
[Service]
Type=oneshot
ExecStart=/usr/bin/echo Hi

[Install]
WantedBy=multi-user.target

From GDB while running systemctl status def@.service:

Program received signal SIGSEGV, Segmentation fault.
0x0000003162a866e1 in __strlen_sse2 () from /lib64/libc.so.6
(gdb) bt
#0  0x0000003162a866e1 in __strlen_sse2 () from /lib64/libc.so.6
#1  0x00000000004a35ea in message_append_basic (m=0xab4b90, type=115 's', p=0xe8458948c0458b48, stored=0x0) at src/libsystemd-bus/bus-message.c:1367
#2  0x00000000004a3927 in sd_bus_message_append_basic (m=0xab4b90, type=115 's', p=0xe8458948c0458b48) at src/libsystemd-bus/bus-message.c:1446
#3  0x00000000004a5d06 in bus_message_append_ap (m=0xab4b90, types=0x50c8b4 "t)", ap=0x7fffae1e2358) at src/libsystemd-bus/bus-message.c:2274
#4  0x00000000004a643f in sd_bus_message_append (m=0xab4b90, types=0x50c8b2 "(st)") at src/libsystemd-bus/bus-message.c:2389
#5  0x0000000000455bb8 in property_get_blockio_device_weight (bus=0x998550, path=0x98c148 "/org/freedesktop/systemd1/unit/def_40_2eservice", 
    interface=0xab4380 "org.freedesktop.systemd1.Scope", property=0x50c90d "BlockIODeviceWeight", reply=0xab4b90, userdata=0x7fffae1e2630, error=0x7fffae1e25a0)
    at src/core/dbus-cgroup.c:52
#6  0x00000000004af335 in invoke_property_get (bus=0x998550, v=0x759df0 <bus_cgroup_vtable+240>, path=0x98c148 "/org/freedesktop/systemd1/unit/def_40_2eservice", 
    interface=0xab4380 "org.freedesktop.systemd1.Scope", property=0x50c90d "BlockIODeviceWeight", reply=0xab4b90, userdata=0x7fffae1e2630, error=0x7fffae1e25a0)
    at src/libsystemd-bus/bus-objects.c:418
#7  0x00000000004afe09 in vtable_append_all_properties (bus=0x998550, reply=0xab4b90, path=0x98c148 "/org/freedesktop/systemd1/unit/def_40_2eservice", 
    c=0xab4330, userdata=0x7fffae1e2630, error=0x7fffae1e25a0) at src/libsystemd-bus/bus-objects.c:658
#8  0x00000000004b0108 in property_get_all_callbacks_run (bus=0x998550, m=0xab4860, first=0xab4130, require_fallback=true, iface=0x0, found_object=0x7fffae1e26cb)
    at src/libsystemd-bus/bus-objects.c:727
#9  0x00000000004b179d in object_find_and_run (bus=0x998550, m=0xab4860, p=0x7fffae1e2670 "/org/freedesktop/systemd1/unit", require_fallback=true, 
    found_object=0x7fffae1e26cb) at src/libsystemd-bus/bus-objects.c:1235
#10 0x00000000004b1bb0 in bus_process_object (bus=0x998550, m=0xab4860) at src/libsystemd-bus/bus-objects.c:1310
#11 0x00000000004ba66d in process_message (bus=0x998550, m=0xab4860) at src/libsystemd-bus/sd-bus.c:2079
#12 0x00000000004ba797 in process_running (bus=0x998550, ret=0x0) at src/libsystemd-bus/sd-bus.c:2107
#13 0x00000000004bad85 in sd_bus_process (bus=0x998550, ret=0x0) at src/libsystemd-bus/sd-bus.c:2270
#14 0x00000000004bb865 in io_callback (s=0x978770, fd=16, revents=1, userdata=0x998550) at src/libsystemd-bus/sd-bus.c:2523
#15 0x00000000004c0c0e in source_dispatch (s=0x978770) at src/libsystemd-bus/sd-event.c:1767
#16 0x00000000004c19c0 in sd_event_run (e=0x978ce0, timeout=18446744073709551615) at src/libsystemd-bus/sd-event.c:2016
#17 0x0000000000411e3a in manager_loop (m=0x9788e0) at src/core/manager.c:1746
#18 0x000000000040b424 in main (argc=4, argv=0x7fffae1e2e98) at src/core/main.c:1650