RFR: JDK-8344907 : NullPointerException in Win32ShellFolder2.getSystemIcon when "icon" is null

[Alexey Ivanov]

On Tue, 17 Dec 2024 00:03:32 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

>> Win32ShellFolder2.getSystemIcon() can result in NPE if icon is null. Sanity null checks have been added.
>> 
>> 
>> long hIcon = getSystemIcon(iconType.getIconID()); //Can return null
>> Image icon = makeIcon(hIcon); // returns null if the condition (hIcon != 0L && hIcon != -1L) is false
>> if (LARGE_ICON_SIZE != icon.getWidth(null)) { // NullPointerException -- icon is null
>> 
>> 
>> Occurs when Windows is unable to provide a system icon and the code assumes an icon will **always** be returned, but the Windows API makes no such guarantee.
>> 
>> getSystemIcon calls LoadIcon (User32.dll). This can return null.
>> https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-loadicona
>
> src/java.desktop/windows/classes/sun/awt/shell/Win32ShellFolder2.java line 1220:
> 
>> 1218:             Image icon = makeIcon(hIcon);
>> 1219:             if (icon != null && size != icon.getWidth(null)) {
>> 1220:                 icon = new MultiResolutionIconImage(size, icon);
> 
> Although `icon != null` check is not strictly required here due to `hIcon != 0` check, added it as sanity check and to be consistent with other locations in Win32ShellFolder2.java where makeIcon() is called (which is followed by a null check for the returned icon).

I'd leave it out here. As @azuev-java [notes above](https://github.com/openjdk/jdk/pull/22776/files#r1887863199), the likely problem is `hIcon == 0` rather than `makeIcon` returns `null`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22776#discussion_r1888602404