export_step fails on moved assembly

[gumyr]

Export is failing:

from build123d import *
from ocp_vscode import *
from bd_warehouse.thread import TrapezoidalThread

testobj = TrapezoidalThread(
    diameter=20,
    pitch=1.5,
    length=20,
    thread_angle=30.0,
)
testobj_moved = testobj.moved(Location((0, 0, 10)))
# show(testobj)
# print("exporting unmoved step")
# export_step(testobj, "test.step")
print("exporting moved step, will fail")
show(testobj_moved)
print(testobj_moved.show_topology())
export_step(testobj_moved, "test.step")

Traceback (most recent call last):
  File "/home/roger-maitland/Documents/build123d/support/x0pherl-2.py", line 18, in <module>
    export_step(testobj_moved, "test.step")
  File "/home/roger-maitland/Documents/build123d/src/build123d/exporters3d.py", line 280, in export_step
    doc = _create_xde(to_export, unit)
  File "/home/roger-maitland/Documents/build123d/src/build123d/exporters3d.py", line 139, in _create_xde
    TDataStd_Name.Set_s(node_label, TCollection_ExtendedString(node.label))
OCP.Standard.Standard_NullObject: A null Label has no attribute.