Decorations: Only call implementation methods when supported. This protects against scenarios where those methods are called regardless of the outcome of #isCustomDecorationSupported e.g. when uninstalling popup decorations.

core/src/main/java/com/github/weisj/darklaf/platform/DecorationsHandler.java

@@ -71,14 +71,17 @@ public class DecorationsHandler {
     }
 
     public CustomTitlePane createTitlePane(final JRootPane rootPane, final int decorationStyle, final Window window) {
+        if (!decorationsProvider.isCustomDecorationSupported()) return DefaultDecorationsProvider.createNoOPTitlePane();
         return decorationsProvider.createTitlePane(rootPane, decorationStyle, window);
     }
 
     public void installPopupWindow(final Window window) {
+        if (!decorationsProvider.isCustomDecorationSupported()) return;
         decorationsProvider.installPopupWindow(window);
     }
 
     public void uninstallPopupWindow(final Window window) {
+        if (!decorationsProvider.isCustomDecorationSupported()) return;
         decorationsProvider.uninstallPopupWindow(window);
     }
 

core/src/main/java/com/github/weisj/darklaf/platform/DefaultDecorationsProvider.java

@@ -32,6 +32,10 @@ import com.github.weisj.darklaf.platform.decorations.DecorationsProvider;
 public class DefaultDecorationsProvider implements DecorationsProvider {
     @Override
     public CustomTitlePane createTitlePane(final JRootPane rootPane, final int decorationStyle, final Window window) {
+        return createNoOPTitlePane();
+    }
+
+    static CustomTitlePane createNoOPTitlePane() {
         return new CustomTitlePane() {
             @Override
             public void uninstall(final boolean removeDecorations) {}

core/src/main/java/com/github/weisj/darklaf/ui/DarkPopupFactory.java

@@ -178,6 +178,8 @@ public class DarkPopupFactory extends PopupFactory {
             rootPane.putClientProperty("Window.shadow", !noDecorations);
         }
         if (noDecorations) {
+            // We also uninstall if decorations aren't enabled/supported as a reused window could be
+            // decorated previously.
             DecorationsHandler.getSharedInstance().uninstallPopupWindow(window);
         } else if (DecorationsHandler.getSharedInstance().isCustomDecorationSupported()) {
             DecorationsHandler.getSharedInstance().installPopupWindow(window);