code: def makeMissingRequiredGlyphs(font, glyphSet):
          
          if ".notdef" in glyphSet:
              return
  
          unitsPerEm = otRound(getAttrWithFallback(font.info, "unitsPerEm"))
          ascender = otRound(getAttrWithFallback(font.info, "ascender"))
          descender = otRound(getAttrWithFallback(font.info, "descender"))
          defaultWidth = otRound(unitsPerEm * 0.5)
          glyphSet[".notdef"] = StubGlyph(name=".notdef",
                                          width=defaultWidth,
                                          unitsPerEm=unitsPerEm,
                                          ascender=ascender,
                                          descender=descender)
docs: Add .notdef to the glyph set if it is not present.
  
          **This should not be called externally.** Subclasses
          may override this method to handle the glyph creation
          in a different way if desired.