Only show visible windows.

Fixed NPE when title is null.

core/src/main/java/com/github/weisj/darklaf/LafManager.java

@@ -192,9 +192,10 @@ public final class LafManager {
             updateLafRecursively(childWindow);
         }
         SwingUtilities.updateComponentTreeUI(window);
-        //  Use custom decorations when supported by the LAF
+        //Ensure decorations are applied appropriately.
+        boolean wasVisible = window.isVisible();
         window.dispose();
-        window.setVisible(true);
+        window.setVisible(wasVisible);
     }
 
     /**

windows/src/main/java/com/github/weisj/darklaf/platform/windows/ui/WindowsTitlePane.java

@@ -637,10 +637,12 @@ public class WindowsTitlePane extends CustomTitlePane {
     }
 
     private boolean hideTitleBar() {
+        String title = titleLabel.getText();
+        if (title == null) title = "";
         return windowHandle == 0
             || (getWindowDecorationStyle() == JRootPane.NONE
             && menuBar == null
-            && titleLabel.getText().length() == 0);
+            && title.length() == 0);
     }
 
     private class TitlePaneLayout implements LayoutManager {