ggplot(hw, aes(x = ageYear, y = heightIn, shape = sex, fill = weightGroup))+geom_point(size=2.5)+ scale_shape_manual(values=c(21,24))+scale_fill_manual(values= c(NA,"black")

, guide = guide_legend(override.aes = list(shape = 21)))

请问guide = guide_legend(override.aes = list(shape = 21))是什么意思，图例的具体用法不懂，请讲解