code: def test_labels_empty(self):
      labels = Labels([])
      plot = mpl_renderer.get_plot(labels)
      artist = plot.handles["artist"]
      self.assertEqual(artist, [])
  
imports: import numpy
  from holoviews.core.dimension import Dimension
  from holoviews.core.options import Cycle
  from holoviews.core.spaces import HoloMap
  from holoviews.element import Labels
  from holoviews.plotting.util import rgb2hex
  from .test_plot import TestMPLPlot, mpl_renderer
label_desc: Use image node_id 2 for calling the TestLabelsPlot obj's underlying member method code with example usage: obj.test_labels_empty() without return types