diff --git a/NEWS.md b/NEWS.md
index 0b346019b0..a6edf8f3b5 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -6,7 +6,7 @@
 
 ## NEW FEATURES
 
-1. `DT[, {...; .(A,B)}]` (when `.()` is the final item of a multi-statement `{...}`) now auto-names the columns `A` and `B` (just like `DT[, .(A,B)]`) rather than `V1` and `V2`, [#2478](https://github.com/Rdatatable/data.table/issues/2478) [#609](https://github.com/Rdatatable/data.table/issues/609). Similarly, `DT[, if (.N>1) .(B), by=A]` now auto-names the column `B` rather than `V1`. Explicit names are unaffected; e.g. `DT[, {... y= ...; .(A=C+y)}, by=...]` named the column `A` before, and still does.
+1. `DT[, {...; .(A,B)}]` (i.e. when `.()` is the final item of a multi-statement `{...}`) now auto-names the columns `A` and `B` (just like `DT[, .(A,B)]`) rather than `V1` and `V2`, [#2478](https://github.com/Rdatatable/data.table/issues/2478) [#609](https://github.com/Rdatatable/data.table/issues/609). Similarly, `DT[, if (.N>1) .(B), by=A]` now auto-names the column `B` rather than `V1`. Explicit names are unaffected; e.g. `DT[, {... y= ...; .(A=C+y)}, by=...]` named the column `A` before, and still does. Thanks also to @renkun-ken for his go-first strong testing which caught an issue not caught by the test suite or by revdep testing, related to NULL being the last item, [#4061](https://github.com/Rdatatable/data.table/issues/4061).
 
 ## BUG FIXES
 
diff --git a/R/data.table.R b/R/data.table.R
index f8de1462c0..780e09029a 100644
--- a/R/data.table.R
+++ b/R/data.table.R
@@ -886,7 +886,7 @@ replace_dot_alias = function(e) {
           return(q) # else empty list is needed for test 468: adding an empty list column
         }
         if (q[[1L]] == '{') {
-          q[[length(q)]] = do_j_names(q[[length(q)]])
+          if (!is.null(q[[qlen<-length(q)]])) q[[qlen]] = do_j_names(q[[qlen]])
           return(q)
         }
         if (q[[1L]] == 'if') {
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index 157e68e8e7..f10fe26ce1 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -16378,6 +16378,8 @@ test(2121.3, DT[ , if (.N > 1L) .(b), by=a], DT[1:2])
 test(2121.4, DT[ , if (.N > 1L) .(b) else .(c=b), by=a], DT[ , .(a, c=b)],
      warning="Different branches of j expression produced different auto-named columns")
 test(2121.5, DT[, .(.N=.N), by=a], data.table(a=c(1,2), .N=2:1)) # user supplied names preside over autoname dropping leading dot
+## { ending in NULL should retain that NULL, #4061
+test(2121.6, DT[ , {.(a, b=b+1); NULL}], NULL)
 
 
 ###################################