code: def test_empty_bars(self):
      bars = Bars([], kdims=["x", "y"], vdims=["z"])
      plot = bokeh_renderer.get_plot(bars)
      plot.initialize_plot()
      source = plot.handles["source"]
      for v in source.data.values():
          self.assertEqual(len(v), 0)
  
imports: import numpy
  from bokeh.models import CategoricalColorMapper, LinearAxis, LinearColorMapper
  from holoviews.core.overlay import NdOverlay, Overlay
  from holoviews.element import Bars
  from holoviews.plotting.bokeh.util import property_to_dict
  from ..utils import ParamLogStream
  from .test_plot import TestBokehPlot, bokeh_renderer
label_desc: Use image node_id 4 for calling the TestBarPlot obj's underlying member method code with example usage: obj.test_empty_bars() without return types