When I check one of my package, I got error:
Error in as.double(y) :
cannot coerce type ‘S4’ to vector of type ‘double’
If I remove the importFrom(graphics, plot) from the NAMESPACE, the error will not show.
The reason is that I did not import S4 method for plot.
1. add stats4 as import package in DESCRIPTION
2. add importMethodsFrom(stats4, plot) in NAMESPACE.