From 861518ad236d9b9a3f41558921f2c39eae40b356 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 8 Dec 2025 14:16:23 +0100
Subject: [PATCH 1/2] improve error message

---
 R/scale-.R | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/R/scale-.R b/R/scale-.R
index 47b63961ea..42bf786c28 100644
--- a/R/scale-.R
+++ b/R/scale-.R
@@ -1339,8 +1339,11 @@ ScaleDiscrete <- ggproto("ScaleDiscrete", Scale,
     pal_match <-
       vec_slice(pal, match(as.character(x), limits, nomatch = vec_size(pal)))
 
-    if (!is.na(na_value)) {
-      vec_slice(pal_match, vec_detect_missing(x)) <- na_value
+    if (!is.na(na_value) && vec_any_missing(x)) {
+      pal_match <- vec_assign(
+        pal_match, vec_detect_missing(x), na_value,
+        x_arg = "palette", value_arg = "na.value"
+      )
     }
     pal_match
   },

From a3bc14a94e833fbd8a594aea59294e3f4d5f0593 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Mon, 8 Dec 2025 14:23:04 +0100
Subject: [PATCH 2/2] add snapshot test

---
 tests/testthat/_snaps/scale-.md |  8 ++++++++
 tests/testthat/test-scale-.R    | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/tests/testthat/_snaps/scale-.md b/tests/testthat/_snaps/scale-.md
index 8c26a8fc9f..570850316b 100644
--- a/tests/testthat/_snaps/scale-.md
+++ b/tests/testthat/_snaps/scale-.md
@@ -20,6 +20,14 @@
 
     The `scale_name` argument of `binned_scale()` is deprecated as of ggplot2 3.5.0.
 
+# mismatch between `na.value` and `palette` throws error
+
+    Code
+      sc$map(x)
+    Condition
+      Error in `vec_assign()`:
+      ! Can't convert `na.value` <double> to match type of `palette` <character>.
+
 # continuous scales warn about faulty `limits`
 
     Code
diff --git a/tests/testthat/test-scale-.R b/tests/testthat/test-scale-.R
index 49ec77652f..80bad5f4eb 100644
--- a/tests/testthat/test-scale-.R
+++ b/tests/testthat/test-scale-.R
@@ -138,6 +138,16 @@ test_that("Using `scale_name` prompts deprecation message", {
 
 })
 
+test_that("mismatch between `na.value` and `palette` throws error", {
+  x <- c("A", "B", "C", NA)
+  sc <- scale_shape_manual(
+    values = c("circle", "triangle", "square"),
+    na.value = 4
+  )
+  sc$train(x)
+  expect_snapshot(sc$map(x), error = TRUE)
+})
+
 # Continuous scales -------------------------------------------------------
 
 test_that("limits with NA are replaced with the min/max of the data for continuous scales", {