SystemError: <method 'autoTrace' of 'fontforge.glyph' objects> returned a result with an error set

[zhenzi0322]

import fontforge

def GlyphSeparation(onLeft, onRight, context):
    imin_y = max(onRight.iminY, onLeft.iminY)
    imax_y = min(onRight.imaxY, onLeft.imaxY)
    if imax_y < imin_y:
        return (0)
    tot, cnt = 0, 0
    j = imin_y
    while j <= imax_y:
        if onRight.left[j] < 32767 and onLeft.right[j] > -32767:
            sep = onRight.left[j] - onLeft.right[j]
            weight = 1.0 / (sep + context.denom)
            weight *= weight
            tot += weight * sep
            cnt += weight
        j += 1
    if cnt != 0:
        tot /= cnt
    return (int(round(tot)))


fontforge.registerGlyphSeparationHook(GlyphSeparation)

font = fontforge.font()
font.ascent = 336
font.descent = 80
font.em = 416


def add_glyph(unicode, svg_path):
    print(unicode)
    g = font.createMappedChar(unicode)
    g.importOutlines(svg_path, scale=False, correctdir=True)
    g.removeOverlap()
    g.autoTrace() 


def main():
    add_glyph(unicode=67, svg_path="static/svg/67.svg")
    add_glyph(unicode=97, svg_path="static/svg/97.svg")
    add_glyph(unicode=104, svg_path="static/svg/104.svg")
    add_glyph(unicode=105, svg_path="static/svg/105.svg")
    add_glyph(unicode=110, svg_path="static/svg/110.svg")
    add_glyph(unicode=111, svg_path="static/svg/111.svg")
    add_glyph(unicode=116, svg_path="static/svg/116.svg")

    font.generate("test.ttf")
    print("success")


if __name__ == '__main__':
    main()

SystemError: <method 'autoTrace' of 'fontforge.glyph' objects> returned a result with an error set.