fix: Honor null_value precedence over deprecated null_values when exporting to CSV (#334)

Author: Yousa-Mirage

R/sink.R

@@ -276,7 +276,7 @@ sink_csv <- function(
       what = "sink_csv_polars(null_values)",
       details = "Use `null_value` instead."
     )
-    if (!identical(null_value, "")) {
+    if (missing(null_value)) {
       null_value <- null_values
     }
   }

R/write.R

@@ -88,7 +88,7 @@ write_csv_polars <- function(
       what = "write_csv_polars(null_values)",
       details = "Use `null_value` instead."
     )
-    if (!identical(null_value, "")) {
+    if (missing(null_value)) {
       null_value <- null_values
     }
   }

tests/testthat/test-sink.R

@@ -26,6 +26,24 @@ test_that("deprecated args in sink_csv()", {
   })
 })
 
+test_that("sink_csv() resolves null_value and null_values correctly", {
+  dat <- as_polars_lf(data.frame(x = c(1, NA), y = c(1, 2)))
+
+  dest_old <- tempfile(fileext = ".csv")
+  expect_warning(
+    sink_csv(dat, dest_old, null_values = "OLD"),
+    "deprecated"
+  )
+  expect_identical(read.csv(dest_old)[2, "x"], "OLD")
+
+  dest_both <- tempfile(fileext = ".csv")
+  expect_warning(
+    sink_csv(dat, dest_both, null_value = "NEW", null_values = "OLD"),
+    "deprecated"
+  )
+  expect_identical(read.csv(dest_both)[2, "x"], "NEW")
+})
+
 test_that("basic behavior with parquet", {
   skip_if_not_installed("nanoparquet")
   dest <- tempfile(fileext = ".parquet")

tests/testthat/test-write.R

@@ -43,6 +43,24 @@ test_that("deprecated args in write_csv_polars()", {
   })
 })
 
+test_that("write_csv_polars() resolves null_value and null_values correctly", {
+  dat <- as_polars_df(data.frame(x = c(1, NA), y = c(1, 2)))
+
+  dest_old <- tempfile(fileext = ".csv")
+  expect_warning(
+    write_csv_polars(dat, dest_old, null_values = "OLD"),
+    "deprecated"
+  )
+  expect_identical(read.csv(dest_old)[2, "x"], "OLD")
+
+  dest_both <- tempfile(fileext = ".csv")
+  expect_warning(
+    write_csv_polars(dat, dest_both, null_value = "NEW", null_values = "OLD"),
+    "deprecated"
+  )
+  expect_identical(read.csv(dest_both)[2, "x"], "NEW")
+})
+
 test_that("basic behavior with IPC", {
   skip_if_not_installed("arrow")
   dest <- tempfile(fileext = ".arrow")