code: def test_vspan_empty(self):
      vline = VSpan(None)
      plot = bokeh_renderer.get_plot(vline)
      span = plot.handles["glyph"]
      self.assertEqual(span.visible, False)
  
imports: import unittest
  import numpy
  import holoviews
  from holoviews.element import Arrow, HLine, HLines, HSpan, HSpans, Labels, Slope, Text, VLine, VLines, VSpan, VSpans
  from holoviews.plotting.bokeh.util import bokeh32, bokeh33
  from .test_plot import TestBokehPlot, bokeh_renderer
label_desc: Use image node_id 6 for calling the TestHVSpanPlot obj's underlying member method code with example usage: obj.test_vspan_empty() without return types