R: ggtree gradient highlight issue

Question

I try to fill two clades with gradient color:

set.seed(123)
tree <- rtree(31)
df   <- data.frame(node=c(47, 36), type=c("A", "B"))
ggtree(tree) + geom_text2(aes(subset=!isTip, label=node), hjust=-.3) +
  geom_hilight(data = df, 
               aes(node = node, fill = type),
               type = "gradient",
               graident.direction = 'rt',
               alpha=.6)

and get an error instead: Error in fix.by(by.x, x)

When I remove 'type = "gradient"' from a code, I get simple solid fill: What's wrong with my code?