migrate to grob utilities

Author: teunbrand

DESCRIPTION

@@ -173,7 +173,6 @@ Collate:
     'ggplot2-package.R'
     'grob-absolute.R'
     'grob-dotstack.R'
-    'grob-null.R'
     'grouping.R'
     'theme-elements.R'
     'guide-.R'

R/grob-null.R

@@ -48,6 +48,17 @@ gg_par <- function(..., stroke = NULL, pointsize = NULL) {
   inject(gpar(!!!args))
 }
 
+#' The zero grob draws nothing and has zero size.
+#'
+#' @keywords internal
+#' @export
+zeroGrob <- function() .zeroGrob
+
+.zeroGrob <- NULL
+on_load(.zeroGrob <- add_class(nullGrob(), "zeroGrob"))
+
+is.zero <- function(x) is.null(x) || inherits(x, "null")
+
 width_cm <- function(x) {
   if (is.grob(x)) {
     convertWidth(grobWidth(x), "cm", TRUE)