Handle null aesthetics when labelling

Fixes #2598

Author: hadley

R/plot-construction.r

@@ -117,7 +117,7 @@ ggplot_add.uneval <- function(object, plot, object_name) {
   # defaults() doesn't copy class, so copy it.
   class(plot$mapping) <- class(object)
 
-  labels <- lapply(object, rlang::quo_name)
+  labels <- lapply(object, function(x) if (is.null(x)) x else rlang::quo_name(x))
   names(labels) <- names(object)
   update_labels(plot, labels)
 }

tests/testthat/test-aes.r

@@ -93,6 +93,11 @@ test_that("quosures are squashed when creating default label for a mapping", {
   expect_identical(p$labels$x, "identity(cyl)")
 })
 
+test_that("labelling doesn't cause error if aesthetic is nul", {
+  p <- ggplot(mtcars) + aes(x = NULL)
+  expect_null(p$labels$x)
+})
+
 
 # Visual tests ------------------------------------------------------------