`GPXTrackSegment`'s `length_2d` marked as `Optional[float]` - can it ever return `None`?

[thomthom]

gpxpy/gpxpy/gpx.py

Lines 755 to 777 in 09fc46b

	def length_2d(self) -> Optional[float]:
	"""
	Computes 2-dimensional length (meters) of segment (only latitude and
	longitude, no elevation).
	Returns
	----------
	length : float
	Length returned in meters
	"""
	return mod_geo.length_2d(self.points) # type: ignore
	def length_3d(self) -> float:
	"""
	Computes 3-dimensional length of segment (latitude, longitude, and
	elevation).
	Returns
	----------
	length : float
	Length returned in meters
	"""
	return mod_geo.length_3d(self.points) # type: ignore

Why is length_2d marked as returning Optional[float]?
length_3d does not. GPXTrack and GPX's versions of length_2d are marked as plain float.

Is this a typings bug? Logic didn't seem to suggest that None is possible.