Issue is observed in JTable demo in SwingSet2 whereby if we set the focus on a table cell (or click on a table cell) and Press Ctrl+F1 (show/hide tooltip) on a cell of JTable then NullpointerException is seen
> Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot > invoke "java.awt.event.MouseEvent.getLocationOnScreen()" because > "this.mouseEvent" is null This is because ToolTip associated with JTable demo button at top of SwingSet2 has MouseMotion Listener which causes [mouseEvent to be null](https://github.com/openjdk/jdk/blame/da3001daf79bf943d6194d9fd60250d519b9680d/src/java.desktop/share/classes/javax/swing/ToolTipManager.java#L573) when mouse exits the demo button area and enter the table cells area where show/hide tooltip causes showTipWindow to be called trying to access `mouseEvent` which is null. Fix is made to check for null in this kind of cases..No regression test is added as it can be checked easily with SwingSet2.. ------------- Commit messages: - 8332431: NullPointerException in JTable of SwingSet2 Changes: https://git.openjdk.org/jdk/pull/19379/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19379&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8332431 Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod Patch: https://git.openjdk.org/jdk/pull/19379.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/19379/head:pull/19379 PR: https://git.openjdk.org/jdk/pull/19379
