Require nnet package to generate from NNETAR models

Resolves #437

Author: mitchelloharawild

R/nnetar.R

@@ -334,6 +334,7 @@ forecast.NNETAR <- function(object, new_data, specials = NULL, simulate = TRUE,
 #'   generate()
 #' @export
 generate.NNETAR <- function(x, new_data, specials = NULL, bootstrap = FALSE, ...) {
+  require_package("nnet")
   # Prepare xreg
   xreg <- specials$xreg[[1]]