Regression with Sankey plot

[harmbuisman]

ALL software version info

Holoviews: 0.13.1
Python: 3.7
Bokeh: 2.0

Description of expected behavior and the observed behavior

Regression with a sankey plot case that was working in 0.12

Case now leads to a ZeroDivisionError.

Complete, minimal, self-contained example code that reproduces the issue

empty = pd.DataFrame({'source':['No data'], 'target':[' No data'], 'count':[1]})
sankey = hv.Sankey(empty)

Stack traceback and/or browser JavaScript console output

215             max_depth = max(depths.values()) - 1 if depths else 1
216             height = self.p.bounds[3] - self.p.bounds[1]

--> 217 py = min((height * 0.1) / max_depth, 20)
218
219 def initializeNodeBreadth():

ZeroDivisionError: float division by zero

Screenshots or screencasts of the bug in action

Expected result which is given by 0.12.7: