diff --git a/DESCRIPTION b/DESCRIPTION
index da78c46c3d..c2116522eb 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -177,7 +177,6 @@ Collate:
     'ggplot2-package.R'
     'grob-absolute.R'
     'grob-dotstack.R'
-    'grob-null.R'
     'grouping.R'
     'properties.R'
     'margins.R'
diff --git a/NAMESPACE b/NAMESPACE
index ce32705b6d..bf4d62e93a 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -20,7 +20,6 @@ S3method(as.list,ggproto)
 S3method(autolayer,default)
 S3method(autoplot,default)
 S3method(c,mapped_discrete)
-S3method(drawDetails,zeroGrob)
 S3method(format,ggproto)
 S3method(format,ggproto_method)
 S3method(format,rd_section_aesthetics)
@@ -52,9 +51,7 @@ S3method(ggplot,default)
 S3method(ggplot_add,default)
 S3method(grid.draw,absoluteGrob)
 S3method(grobHeight,absoluteGrob)
-S3method(grobHeight,zeroGrob)
 S3method(grobWidth,absoluteGrob)
-S3method(grobWidth,zeroGrob)
 S3method(grobX,absoluteGrob)
 S3method(grobY,absoluteGrob)
 S3method(guide_gengrob,default)
@@ -63,7 +60,6 @@ S3method(guide_merge,default)
 S3method(guide_train,default)
 S3method(guide_transform,default)
 S3method(heightDetails,titleGrob)
-S3method(heightDetails,zeroGrob)
 S3method(limits,Date)
 S3method(limits,POSIXct)
 S3method(limits,POSIXlt)
@@ -117,7 +113,6 @@ S3method(vec_ptype2,mapped_discrete.factor)
 S3method(vec_ptype2,mapped_discrete.integer)
 S3method(vec_ptype2,mapped_discrete.mapped_discrete)
 S3method(widthDetails,titleGrob)
-S3method(widthDetails,zeroGrob)
 export("%+%")
 export("%+replace%")
 export(.data)
diff --git a/NEWS.md b/NEWS.md
index 829d029bb5..7fab21a27a 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # ggplot2 (development version)
 
+* (internal) `zeroGrob()` now returns a `grid::nullGrob()` (#6390).
 * `stat_ydensity()` now only requires the `x` or `y` aesthetic. The other will
   be populated with 0, similar to `stat_boxplot()` (@teunbrand, #6600)
 * Implemented `as.list()` and `S7::convert()` methods for lists and classes in ggplot2 
diff --git a/R/aes-variants.R b/R/aes-variants.R
index 264151f2bb..12851c5cd6 100644
--- a/R/aes-variants.R
+++ b/R/aes-variants.R
@@ -113,8 +113,7 @@ aes_all <- function(vars) {
   # Quosure the symbols in the empty environment because they can only
   # refer to the data mask
   x <- class_mapping(lapply(vars, function(x) new_quosure(as.name(x), emptyenv())))
-  class(x) <- union("unlabelled", class(x))
-  x
+  add_class(x, "unlabelled")
 }
 
 #' Automatic aesthetic mapping
diff --git a/R/grob-null.R b/R/grob-null.R
deleted file mode 100644
index da32009b3b..0000000000
--- a/R/grob-null.R
+++ /dev/null
@@ -1,26 +0,0 @@
-#' The zero grob draws nothing and has zero size.
-#'
-#' @keywords internal
-#' @export
-zeroGrob <- function() .zeroGrob
-
-.zeroGrob <- NULL
-on_load(.zeroGrob <- grob(cl = "zeroGrob", name = "NULL"))
-
-#' @export
-#' @method widthDetails zeroGrob
-widthDetails.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method heightDetails zeroGrob
-heightDetails.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method grobWidth zeroGrob
-grobWidth.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method grobHeight zeroGrob
-grobHeight.zeroGrob <- function(x) unit(0, "cm")
-#' @export
-#' @method drawDetails zeroGrob
-drawDetails.zeroGrob <- function(x, recording) {}
-
-is_zero <- function(x) is.null(x) || inherits(x, "zeroGrob")
diff --git a/R/theme.R b/R/theme.R
index 79143ec0b5..d263ff0fe6 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -501,7 +501,7 @@ theme <- function(...,
   }
 
   t <- class_theme(elements, complete = complete, validate = validate)
-  class(t) <- union("theme", class(t))
+  t <- add_class(t, "theme")
   t
 }
 
diff --git a/R/utilities-grid.R b/R/utilities-grid.R
index 4713d62893..a6fdf81fed 100644
--- a/R/utilities-grid.R
+++ b/R/utilities-grid.R
@@ -53,6 +53,17 @@ 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)
diff --git a/R/utilities.R b/R/utilities.R
index 93464a89af..e42a72c8cb 100644
--- a/R/utilities.R
+++ b/R/utilities.R
@@ -942,6 +942,15 @@ compute_data_size <- function(data, size, default = 0.9,
   data
 }
 
+add_class <- function(x, new_class) {
+  new_class <- setdiff(new_class, class(x))
+  if (length(new_class) < 1) {
+    return(x)
+  }
+  class(x) <- union(new_class, class(x))
+  x
+}
+
 try_prop <- function(object, name, default = NULL) {
   if (!S7::S7_inherits(object)) {
     return(default)
diff --git a/man/zeroGrob.Rd b/man/zeroGrob.Rd
index e4aac88eb0..6fcfe56218 100644
--- a/man/zeroGrob.Rd
+++ b/man/zeroGrob.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/grob-null.R
+% Please edit documentation in R/utilities-grid.R
 \name{zeroGrob}
 \alias{zeroGrob}
 \title{The zero grob draws nothing and has zero size.}
diff --git a/tests/testthat/_snaps/theme-elements.md b/tests/testthat/_snaps/theme-elements.md
index f3931ef6b0..936112d821 100644
--- a/tests/testthat/_snaps/theme-elements.md
+++ b/tests/testthat/_snaps/theme-elements.md
@@ -64,10 +64,8 @@
 ---
 
     Code
-      element_grob(el, label = element_blank())
+      x <- element_grob(el, label = element_blank())
     Condition
       Warning:
       `label` cannot be a <ggplot2::element_blank> object.
-    Output
-      zeroGrob[NULL] 
 
diff --git a/tests/testthat/test-facet-.R b/tests/testthat/test-facet-.R
index b93b8237ab..e09caa2d99 100644
--- a/tests/testthat/test-facet-.R
+++ b/tests/testthat/test-facet-.R
@@ -160,7 +160,7 @@ test_that("strips can be removed", {
     theme(strip.background = element_blank(), strip.text = element_blank())
   g_grobs <- ggplotGrob(g)
   strip_grobs <- g_grobs$grobs[grepl('strip-', g_grobs$layout$name)]
-  expect_true(all(sapply(strip_grobs, inherits, 'zeroGrob')))
+  expect_true(all(sapply(strip_grobs, inherits, 'null')))
 })
 
 test_that("strip clipping can be set from the theme", {
diff --git a/tests/testthat/test-stat-density2d.R b/tests/testthat/test-stat-density2d.R
index 43a99e9513..2e2896cc47 100644
--- a/tests/testthat/test-stat-density2d.R
+++ b/tests/testthat/test-stat-density2d.R
@@ -100,5 +100,5 @@ test_that("stat_density_2d handles faulty bandwidth", {
   p <- ggplot(faithful, aes(eruptions, waiting)) +
     stat_density_2d(h = c(0, NA))
   expect_snapshot_warning(b <- ggplot_build(p))
-  expect_s3_class(layer_grob(b)[[1]], "zeroGrob")
+  expect_s3_class(layer_grob(b)[[1]], "null")
 })
diff --git a/tests/testthat/test-theme-elements.R b/tests/testthat/test-theme-elements.R
index d74b35b5c3..76ef1ae7cd 100644
--- a/tests/testthat/test-theme-elements.R
+++ b/tests/testthat/test-theme-elements.R
@@ -100,7 +100,7 @@ test_that("element_text throws appropriate conditions", {
   # labs(y = element_blank()) for some reason
   el <- theme_get()$text
   expect_snapshot(
-    element_grob(el, label = element_blank())
+    x <- element_grob(el, label = element_blank())
   )
 })