old_contents: # -*- coding: utf-8 -*-
  from blockdiag.noderenderer import NodeShape
  from blockdiag.noderenderer import install_renderer
  from blockdiag.utils.XY import XY
  
  
  class NoneBox(NodeShape):
      def render_shape(self, drawer, format, **kwargs):
          outline = kwargs.get('outline')
          fill = kwargs.get('fill')
  
          box = self.metrix.cell(self.node).box()
          if self.node.background:
              drawer.rectangle(box, fill=self.node.color,
                               outline=self.node.color)
              drawer.loadImage(self.node.background, self.textbox)
  
  
  def setup(self):
      install_renderer('textbox', NoneBox)
  
new_contents: # -*- coding: utf-8 -*-
  from blockdiag.noderenderer import NodeShape
  from blockdiag.noderenderer import install_renderer
  from blockdiag.utils.XY import XY
  
  
  class TextBox(NodeShape):
      def render_shape(self, drawer, format, **kwargs):
          outline = kwargs.get('outline')
          fill = kwargs.get('fill')
  
          box = self.metrix.cell(self.node).box()
          if self.node.background:
              drawer.rectangle(box, fill=self.node.color,
                               outline=self.node.color)
              drawer.loadImage(self.node.background, self.textbox)
  
  
  def setup(self):
      install_renderer('textbox', TextBox)
  
subject: change class name.