SVG generation fails if tasks with dependencies do not define duration (and use start, stop instead)

[TimoL]

If I include a list of tasks create via "Task(start=..., stop=...)" in a gantt project and add dependencies between these tasks, svg generation will fail with:

File "/Users/Q479089/cc/deploy-roadmap-image-roadmap/.venv/lib/python3.9/site-packages/gantt/gantt.py", line 1829, in make_svg_for_tasks
    psvg, pheight = self.svg(prev_y=2, start=start_date, end=end_date, color = self.color, scale=scale, title_align_on_left=title_align_on_left, offset=offset)
  File "/Users/Q479089/cc/deploy-roadmap-image-roadmap/.venv/lib/python3.9/site-packages/gantt/gantt.py", line 2121, in svg
    trepr, theight = t.svg(cy, start=start, end=end, color=color, level=level+1, scale=scale, title_align_on_left=title_align_on_left, offset=offset)
  File "/Users/Q479089/cc/deploy-roadmap-image-roadmap/.venv/lib/python3.9/site-packages/gantt/gantt.py", line 950, in svg
    if self.start is not None and self.start_date() != self.start:
  File "/Users/Q479089/cc/deploy-roadmap-image-roadmap/.venv/lib/python3.9/site-packages/gantt/gantt.py", line 740, in start_date
    if t.end_date() >= prev_task_end:
  File "/Users/Q479089/cc/deploy-roadmap-image-roadmap/.venv/lib/python3.9/site-packages/gantt/gantt.py", line 883, in end_date
    while duration > 1 or (current_day.weekday() in _not_worked_days() or current_day in VACATIONS):
TypeError: '>' not supported between instances of 'NoneType' and 'int'

Obviously the duration is not defined, if the start and stop parameters were used for task creation.