src/jdk.scripting.nashorn.shell/share/classes/jdk/nashorn/tools/jjs/NashornCompleter.java

@@ -252,10 +252,15 @@
 
     // Internals only below this point
 
     // read file name from the user using by showing a swing file chooser diablog
     private static String readFileName(final PrintWriter err) {
+        // if running on AWT Headless mode, don't attempt swing dialog box!
+        if (Main.HEADLESS) {
+            return null;
+        }
+
         final FutureTask<String> fileChooserTask = new FutureTask<String>(() -> {
             // show a file chooser dialog box
             final JFileChooser chooser = new JFileChooser();
             chooser.setFileFilter(new FileNameExtensionFilter("JavaScript Files", "js"));
             final int retVal = chooser.showOpenDialog(null);