Do not allow NA as column name

NEWS.md

@@ -22,6 +22,7 @@
 * `writeData()` calls `force(x)` to evaluate the object before options are set ([#264](https://github.com/ycphs/openxlsx/issues/264))
 * `createComment()` now correctly handles `integers` in `width` and `height` ([#275](https://github.com/ycphs/openxlsx/issues/275))
 * `setStyles()` accepts `halign="justify"` ([#305](https://github.com/ycphs/openxlsx/issues/305))
+* `data.frame`s with `NA` column names are converted to `"NA"` when saving ([#292](https://github.com/ycphs/openxlsx/issues/292), [#316](https://github.com/ycphs/openxlsx/issues/316)
 
 # openxlsx 4.2.4
 

R/writeData.R

@@ -180,6 +180,8 @@ writeData <- function(
 ) {
 
   x <- force(x)
+  # transforms NA to "NA" for bad names
+  names(x) <- paste(names(x))
 
   op <- get_set_options()
   on.exit(options(op), add = TRUE)

tests/testthat/test-writeData.R

@@ -35,3 +35,17 @@ test_that("writeData() forces evaluation of x (#264)", {
   options(op)
   file.remove(wbfile)
 })
+
+test_that("colnames with NA are appropriately handled [292]", {
+  x <- data.frame(a = 1, b = 2)
+  colnames(x) <- c("a", NA)
+  wbfile <- temp_xlsx()
+  wb <- buildWorkbook(x)
+  wb$worksheets[[1]]$sheet_data
+  saveWorkbook(wb, wbfile)
+
+  # what could I look for 
+  # openXL(wb)
+  # openXL(wbfile)
+  # read.xlsx(wbfile)
+})