don't treat the no data case differently

Author: basnijholt

adaptive/learner/learner1D.py

@@ -590,12 +590,10 @@ def plot(self):
             Plot of the evaluated data.
         """
         hv = ensure_holoviews()
-        if not self.data:
-            p = hv.Scatter([]) * hv.Path([])
-        elif not self.vdim > 1:
+        if self.vdim <= 1:
             p = hv.Scatter(self.data) * hv.Path([])
         else:
-            xs, ys = zip(*sorted(self.data.items()))
+            xs, ys = zip(*sorted(self.data.items())) if self.data else [], []
             p = hv.Path((xs, ys)) * hv.Scatter([])
 
         # Plot with 5% empty margins such that the boundary points are visible