autoplot.generic_spct: Warn if plot methods is called.
Description
No automatic plot method is possible for objects of class geenric_spct
as this class is meant to be used only as a pure base class for derivation.
Usage
# S3 method for generic_spct
autoplot(object, ...)# S3 method for generic_mspct
autoplot(object, ...)
Value
an empty ggplot object.