In 2.1.0:
DF <- data.frame(x=rnorm(1000), y=rnorm(1000))
ggplot(DF) + geom_hex(aes(x=x, y=y, fill=..density..))
causes error:
Error in eval(expr, envir, enclos) : object 'density' not found
But in 2.0.0 (or other older versions), we get (random seeds notwithstanding):
