当只使用系列和比例计数中的两个值时，小提琴会产生空图

Question

当系列中只有两个值和使用的比例计数时，我的小提琴图会产生一个空图。

library(ggplot2)
d1 <- data.frame(x=c("a","a","a","b","b","b"),y=c(1,2,2,1,2,1)) # Two series of three with different values through each series
d2 <- data.frame(x=c("a","a","a","b","b"),    y=c(1,2,2,1,2))   # Two series, one of three, one of two with different values through each series
ggplot(data=d1) + geom_violin(aes(x=x,y=y))                     # This works
ggplot(data=d1) + geom_violin(aes(x=x,y=y), scale="count")      # This works
ggplot(data=d2) + geom_violin(aes(x=x,y=y))                     # This works
ggplot(data=d2) + geom_violin(aes(x=x,y=y), scale="count")      # This produces an empty plot

前三个工作正常。第四个产生一个空图。这是一个错误吗？有解决方法吗？ 感谢