/** writes safely (to temp file, then rename) */
static File saveTextFile(String fileName, String contents) throws IOException {
  /*ifdef CriticalActions
  temp beginCriticalAction("Saving file " + fileName + " (" + l(contents) + " chars)");
  endifdef*/
  
  File file = new File(fileName);
  mkdirsForFile(file);
  String tempFileName = fileName + "_temp";
  File tempFile = new File(tempFileName);
  if (contents != null) {
    if (tempFile.exists()) try {
      S saveName = tempFileName + ".saved." + now();
      copyFile(tempFile, new File(saveName));
    } catch (Throwable e) { printStackTrace(e); }
    temp FileOutputStream fileOutputStream = newFileOutputStream(tempFile.getPath());
    OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream, "UTF-8");
    PrintWriter printWriter = new PrintWriter(outputStreamWriter);
    printWriter.print(contents);
    printWriter.close();
  }
  
  if (file.exists() && !file.delete())
    throw new IOException("Can't delete " + fileName);

  if (contents != null)
    if (!tempFile.renameTo(file))
      throw new IOException("Can't rename " + tempFile + " to " + file);
      
  ifndef LeanMode
  vmBus_send('wroteFile, file);
  endifndef
  ret file;
}

static File saveTextFile(File fileName, String contents) ctex {
  saveTextFile(fileName.getPath(), contents);
  ret fileName;
}

Began life as a copy of #2000323

Can now handle "null" contents (deletes file)