`(*PrettyPrint) Export()` needs to return error in order to conform to the `Exporter` interface and be used as an exporter. Without this change, trying to use the PrettyPrint exporter results in this compile error:
cannot use &export.PrettyPrint{} (value of type *export.PrettyPrint) as type export.Exporter in array or slice literal:
*export.PrettyPrint does not implement export.Exporter (wrong type for Export method)
have Export(exports chan interface{})
want Export(exports chan interface{}) error
