Sampling bias layer

Hi,

I was looking up information on how to construct a bias layer for sampling bias and found this: https://scottrinnan.wordpress.com/2015/08/31/how-to-construct-a-bias-file-with-r-for-use-in-maxent-modeling/.
However, this method does not seem to be working. Is the biasfile arg not working (anymore) ?
`mod1 <- maxent(climdat, occurrences, args = "biasfile=dens.ras")`
 
Best regards,
Pablo