Stack trace:

#0  g_hash_table_lookup_node (hash_return=<synthetic pointer>, key=0x7fb2b801b010, hash_table=0x7fb2b00026a0)
    at /build/buildd/glib2.0-2.34.1/./glib/ghash.c:410
#1  g_hash_table_remove_internal (hash_table=0x7fb2b00026a0, key=0x7fb2b801b010, notify=1)
    at /build/buildd/glib2.0-2.34.1/./glib/ghash.c:1269
#2  0x00007fb2ce526a5d in cal_backend_contacts_remove_book_record (cbc=0x12da0e0, source=0x7fb2b801b010)
    at e-cal-backend-contacts.c:231
#3  0x00007fb2d5e885c4 in g_cclosure_marshal_VOID__OBJECTv (closure=0x12e4950, return_value=<optimized out>, 
    instance=0x12b7dc0, args=<optimized out>, marshal_data=<optimized out>, n_params=<optimized out>, 
    param_types=0x12b5b70) at /build/buildd/glib2.0-2.34.1/./gobject/gmarshal.c:1312
#4  0x00007fb2d5e85407 in _g_closure_invoke_va (closure=0x12e4950, return_value=0x0, instance=0x12b7dc0, 
    args=0x7fffdb2e0a38, n_params=1, param_types=0x12b5b70)
    at /build/buildd/glib2.0-2.34.1/./gobject/gclosure.c:840
#5  0x00007fb2d5e9ddf6 in g_signal_emit_valist (instance=0x12b7dc0, signal_id=<optimized out>, detail=0, 
    var_args=var_args@entry=0x7fffdb2e0a38) at /build/buildd/glib2.0-2.34.1/./gobject/gsignal.c:3211
#6  0x00007fb2d5e9e642 in g_signal_emit (instance=instance@entry=0x12b7dc0, signal_id=<optimized out>, 
    detail=detail@entry=0) at /build/buildd/glib2.0-2.34.1/./gobject/gsignal.c:3356
#7  0x00007fb2d6363bb9 in source_registry_remove_source (source=0x7fb2b801b010, registry=0x12b7dc0)
    at e-source-registry.c:605
#8  source_registry_object_removed_idle_cb (user_data=<optimized out>) at e-source-registry.c:656
#9  0x00007fb2d5bc4ab5 in g_main_dispatch (context=0x12ac680) at /build/buildd/glib2.0-2.34.1/./glib/gmain.c:2715
#10 g_main_context_dispatch (context=context@entry=0x12ac680) at /build/buildd/glib2.0-2.34.1/./glib/gmain.c:3219
#11 0x00007fb2d5bc4de8 in g_main_context_iterate (context=0x12ac680, block=block@entry=1, 
    dispatch=dispatch@entry=1, self=<optimized out>) at /build/buildd/glib2.0-2.34.1/./glib/gmain.c:3290
#12 0x00007fb2d5bc51e2 in g_main_loop_run (loop=0x12ac7e0) at /build/buildd/glib2.0-2.34.1/./glib/gmain.c:3484
#13 0x00007fb2d65b7de8 in dbus_server_run_server (server=0x12ad020) at e-dbus-server.c:222
#14 0x00007fb2d37a5bb8 in ffi_call_unix64 () from /usr/lib/x86_64-linux-gnu/libffi.so.6
#15 0x00007fb2d37a55c0 in ffi_call () from /usr/lib/x86_64-linux-gnu/libffi.so.6
#16 0x00007fb2d5e8612b in g_cclosure_marshal_generic_va (closure=0x12ab990, return_value=0x7fffdb2e1000, 
    instance=0x12ad020, args_list=<optimized out>, marshal_data=0x7fb2d65b7d70 <dbus_server_run_server>, 
    n_params=0, param_types=0x0) at /build/buildd/glib2.0-2.34.1/./gobject/gclosure.c:1550
#17 0x00007fb2d5e85407 in _g_closure_invoke_va (closure=0x12ab990, return_value=0x7fffdb2e1000, 
    instance=0x12ad020, args=0x7fffdb2e11a8, n_params=0, param_types=0x0)
    at /build/buildd/glib2.0-2.34.1/./gobject/gclosure.c:840
#18 0x00007fb2d5e9ddf6 in g_signal_emit_valist (instance=0x12ad020, signal_id=<optimized out>, detail=0, 
    var_args=var_args@entry=0x7fffdb2e11a8) at /build/buildd/glib2.0-2.34.1/./gobject/gsignal.c:3211
#19 0x00007fb2d5e9e642 in g_signal_emit (instance=instance@entry=0x12ad020, signal_id=<optimized out>, 
    detail=detail@entry=0) at /build/buildd/glib2.0-2.34.1/./gobject/gsignal.c:3356
#20 0x00007fb2d65b808a in e_dbus_server_run (server=server@entry=0x12ad020, wait_for_client=0)
    at e-dbus-server.c:396
#21 0x0000000000400c2f in main (argc=1, argv=0x7fffdb2e13b8) at evolution-calendar-factory.c:137