diff --git a/R/assert.R b/R/assert.R
index 71e6d08..626ad7f 100644
--- a/R/assert.R
+++ b/R/assert.R
@@ -77,14 +77,16 @@ needs <- assert_package
 #' @param x An object to be checked.
 #' @param expected An appropriate expected value.
 #' @param allow_empty A [`logical`] scalar: should [empty][is_empty()] object be
-#'  allowed?
-#' @param empty Deprecated.
+#'  ignored?
+#' @param allow_null A [`logical`] scalar: should `NULL` object be ignored?
 #' @return
 #'  Throws an error, if any, and returns `x` invisibly otherwise.
 #' @author N. Frerebeau
 #' @family checking methods
 #' @export
-assert_length <- function(x, expected, allow_empty = empty, empty = FALSE) {
+assert_length <- function(x, expected, allow_empty = FALSE, allow_null = FALSE) {
+  if (is.null(x) && isTRUE(allow_null)) return(invisible(NULL))
+
   arg <- deparse(substitute(x))
   if (!(allow_empty && is_empty(x)) && !has_length(x, n = expected)) {
     txt <- tr_("%s must be of length %d; not %d.")
@@ -312,7 +314,7 @@ assert_unique <- function(x) {
 #'  "`integer`", "`double`", "`character`" or "`logical`".
 #' @param allow_empty A [`logical`] scalar: should [empty][is_empty()] object be
 #'  allowed?
-#' @param allow_null A [`logical`] scalar: should `NULL` object be allowed?
+#' @param allow_null A [`logical`] scalar: should `NULL` object be ignored?
 #' @return
 #'  Throws an error, if any, and returns `x` invisibly otherwise.
 #' @author N. Frerebeau
diff --git a/inst/tinytest/test_assert.R b/inst/tinytest/test_assert.R
index 5967672..65a8bd2 100644
--- a/inst/tinytest/test_assert.R
+++ b/inst/tinytest/test_assert.R
@@ -49,6 +49,7 @@ expect_inherits(cnd[[1]], "error_bad_length")
 
 expect_identical(assert_length(numeric(), expected = 10, allow_empty = TRUE), numeric())
 expect_identical(assert_length(LETTERS, expected = 26), LETTERS)
+expect_null(assert_length(NULL, expected = 10, allow_null = TRUE))
 
 ## Lengths ---------------------------------------------------------------------
 k <- list(1:10, 1:20)
diff --git a/man/assert_length.Rd b/man/assert_length.Rd
index 41401da..e9a55ba 100644
--- a/man/assert_length.Rd
+++ b/man/assert_length.Rd
@@ -5,7 +5,7 @@
 \alias{assert_lengths}
 \title{Check Object Length(s)}
 \usage{
-assert_length(x, expected, allow_empty = empty, empty = FALSE)
+assert_length(x, expected, allow_empty = FALSE, allow_null = FALSE)
 
 assert_lengths(x, expected)
 }
@@ -15,9 +15,9 @@ assert_lengths(x, expected)
 \item{expected}{An appropriate expected value.}
 
 \item{allow_empty}{A \code{\link{logical}} scalar: should \link[=is_empty]{empty} object be
-allowed?}
+ignored?}
 
-\item{empty}{Deprecated.}
+\item{allow_null}{A \code{\link{logical}} scalar: should \code{NULL} object be ignored?}
 }
 \value{
 Throws an error, if any, and returns \code{x} invisibly otherwise.
diff --git a/man/assert_type.Rd b/man/assert_type.Rd
index 5fec80a..da5dd33 100644
--- a/man/assert_type.Rd
+++ b/man/assert_type.Rd
@@ -22,7 +22,7 @@ type. It must be one of "\code{list}", "\code{atomic}", "\code{vector}", "\code{
 \item{allow_empty}{A \code{\link{logical}} scalar: should \link[=is_empty]{empty} object be
 allowed?}
 
-\item{allow_null}{A \code{\link{logical}} scalar: should \code{NULL} object be allowed?}
+\item{allow_null}{A \code{\link{logical}} scalar: should \code{NULL} object be ignored?}
 }
 \value{
 Throws an error, if any, and returns \code{x} invisibly otherwise.