`expression(list())` introduced when using labeller in facet

When I am using labeller in facet_wrap I am getting expression(list()) showing up with ggplotly.

mtcars$cyl2 <- factor(mtcars$cyl, labels = c("alpha", "beta", "gamma"))
p <- ggplot(mtcars, aes(wt, mpg)) + geom_point()

ggplotly(p + facet_wrap(. ~cyl)) # See figure 1

ggplotly(p + facet_wrap(. ~cyl, labeller = label_wrap_gen(width = 25, multi_line = FALSE))) #see figure2

Figure 1

Figure 2

首先使用 ggplotly、facet_wrap 和 label_wrap_gen 运行 issue 中的 R 复现，然后比较附带的两张图。跟踪 labeller 的输出在何处变成 facet 标签；完成标准是第二个示例不再显示 expression(list())，并且仍然保留预期的换行标签。