diff --git a/R/scale-type.R b/R/scale-type.R
index 6b292b0e18..921847bf5e 100644
--- a/R/scale-type.R
+++ b/R/scale-type.R
@@ -1,4 +1,8 @@
-find_scale <- function(aes, x, env) {
+find_scale <- function(aes, x, env = parent.frame()) {
+  if (is.null(x)) {
+    return(NULL)
+  }
+
   type <- scale_type(x)
   candidates <- paste("scale", aes, type, sep = "_")
 
diff --git a/R/scales-.r b/R/scales-.r
index 79a3344cae..c185cf95df 100644
--- a/R/scales-.r
+++ b/R/scales-.r
@@ -97,6 +97,7 @@ scales_add_defaults <- function(scales, data, aesthetics, env) {
   if (is.null(new_aesthetics)) return()
 
   datacols <- lapply(aesthetics[new_aesthetics], rlang::eval_tidy, data = data)
+  datacols <- compact(datacols)
 
   for (aes in names(datacols)) {
     scales$add(find_scale(aes, datacols[[aes]], env))
diff --git a/tests/testthat/test-scale-type.R b/tests/testthat/test-scale-type.R
new file mode 100644
index 0000000000..e5b145b1f1
--- /dev/null
+++ b/tests/testthat/test-scale-type.R
@@ -0,0 +1,12 @@
+context("test-scale-type.R")
+
+test_that("no scale for NULL aesthetic", {
+  expect_equal(find_scale("colour", NULL), NULL)
+})
+
+test_that("message + continuous for unknown type", {
+  x <- structure(1:10, class = "ggplot2_foo")
+
+  expect_message(scale <- find_scale("colour", x), "ggplot2_foo")
+  expect_s3_class(scale, "ScaleContinuous")
+})