code: def ufo_create_background_layer_for_all_glyphs(ufo_font):
      # type: (defcon.Font) -> None
      
  
      if "public.background" in ufo_font.layers:
          background = ufo_font.layers["public.background"]
      else:
          background = ufo_font.newLayer("public.background")
  
      for glyph in ufo_font:
          if glyph.name not in background:
              background.newGlyph(glyph.name)
docs: Create a background layer for all glyphs in ufo_font if not present to
      reduce roundtrip differences.