如何在holoviews + bokeh中获得带有图例标签的全高垂直线？

import holoviews as hv
from bokeh.models import Span
from bokeh.plotting import show

vline = Span(dimension='height', line_color='red', line_dash='dashed', line_width=2)

fig = hv.render(hv.Curve([]))  # 创建一个空的图表
fig.renderers.extend([vline])  # 将垂直线对象添加到图表中

fig.legend.append(('Label', [vline]))  # 添加图例标签，'Label'为标签名称

show(fig)