Passing curves to supply() and demand() causes error

[andreagolfari]

I love this package and I thank you very much for it. However, I am unable to pass a data.frame to supply() and demand() to override the sample curves. When I try to do so I receive this error:

Error in `geom_line()`:
! Problem while computing aesthetics.
ℹ Error occurred in the 1st layer.
Caused by error in `FUN()`:
! object 'y' not found

Note that the same is not true for sdcurve(): passing a data.frame with x and y columns works perfectly there.

It would be awesome if you could write an example on how to achieve the desired behavior in supply() and demand().