code: def test_overlay_empty_element_extent(self):
      overlay = Curve([]).redim.range(x=(-10, 10)) * Scatter(
          []
      ).redim.range(y=(-20, 20))
      plot = mpl_renderer.get_plot(overlay)
      extents = plot.get_extents(overlay, {})
      self.assertEqual(extents, (-10, -20, 10, 20))
  
imports: import numpy
  from holoviews.core import DynamicMap, HoloMap, NdOverlay, Overlay
  from holoviews.element import Curve, Scatter
  from ...utils import LoggingComparisonTestCase
  from .test_plot import TestMPLPlot, mpl_renderer
label_desc: Use image node_id 6 for calling the TestOverlayPlot obj's underlying member method code with example usage: obj.test_overlay_empty_element_extent() without return types