TypeError: '<=' not supported between instances of 'NoneType' and 'datetime.datetime' (Stonesoup/plotter)

Question

I am going through the Stone Soup tutorial. I ran the following code

# Plot the results of Truth Path
from stonesoup.plotter import AnimatedPlotterly
plotter = AnimatedPlotterly(timesteps, tail_length=0.3)
plotter.plot_ground_truths(truth, [0, 2])
plotter.fig

And got the following error

   1783 traces_.append(trace_base)
   1785 for n, truth in enumerate(truths):
   1786     # all truth points that come at or before the frame time
-> 1787     t_upper = [data[n]["time"] <= frame_time]
   1789     # only select detections that come after the time cut-off
   1790     t_lower = [data[n]["time"] >= cutoff_time]

TypeError: '<=' not supported between instances of 'NoneType' and 'datetime.datetime'

Are there any fix to this issue? I am running this in Python 3.11 in Anaconda, if that helps.