Index: src/main/java/common/javax/swing/plaf/basic/BasicInternalFrameUI.java =================================================================== --- src/main/java/common/javax/swing/plaf/basic/BasicInternalFrameUI.java (revision 490131) +++ src/main/java/common/javax/swing/plaf/basic/BasicInternalFrameUI.java (working copy) @@ -573,6 +573,10 @@ } protected JComponent createNorthPane(final JInternalFrame f) { + if (f == null) { + throw new NullPointerException(); + } + titlePane = new BasicInternalFrameTitlePane(f); return titlePane; }