render_bounding_box fail on polyline with no vertex

[wickeat]

The image util function render_bounding_box throws a ValueError: not enough values to unpack (expected 2, got 0) exception if the polyline to render has no vertex.

eta/eta/core/image.py

Lines 1116 to 1125 in f45e571

	def render_bounding_box(polyline):
	"""Renders a tight BoundingBox around the given Polyline.
	Args:
	polyline: a Polyline
	Returns:
	a BoundingBox
	"""
	xx, yy = zip(*list(itertools.chain(*polyline.points)))

This happens since a Polyline can contain no vertex.

eta/eta/core/polylines.py

Lines 110 to 113 in f45e571

	@property
	def has_vertices(self):
	"""Whether the polyline has at least one vertex."""
	return any(bool(shape) for shape in self.points)

[brimoor]

Thanks for catching! This will be fixed by #642 and available in fiftyone>1.2.