SWT standalone app fails to start with NPE "org.eclipse.core.runtime.Platform.getOS()" is null

[jeffecom]

I have a large SWT app, which worked fine for years, but when I updated to Eclipse 2025-12 and used the jars from it's plugins folder, the app crashes when it tries to display the first main form.

Cannot invoke "String.equals(Object)" because the return value of "org.eclipse.core.runtime.Platform.getOS()" is null

java.lang.NullPointerException
at org.eclipse.core.runtime.Platform$OS.is(Platform.java:82)
at org.eclipse.core.runtime.Platform$OS.isWindows(Platform.java:89)
at org.eclipse.ui.forms.widgets.ExpandableComposite$ExpandableLayout.layout(ExpandableComposite.java:294)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1333)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1339)
at org.eclipse.swt.widgets.Composite.updateLayout(Composite.java:1318)
at org.eclipse.swt.widgets.Composite.layout(Composite.java:698)
at org.eclipse.swt.widgets.Display.runSettings(Display.java:4221)
at org.eclipse.swt.widgets.Display.messageProc(Display.java:3370)
at org.eclipse.swt.internal.win32.OS.DispatchMessage(Native Method)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3748)

Is has these jars on the classpath.

There was a runtime arg that worked once when I tried it (AI told me, but seems to have forgot).

Is there a way to fix this? It works fine in previous versions of SWT.

[akurtakov]

Transfered as the exception comes from org.eclipse.ui.forms so not an SWT problem. Without a reproducer, I can't help more here.

[akurtakov]

Most likely the problem comes from #2986 but this is 7 months ago so you haven't updated from 2025-09?

[jeffecom]

Thanks for that.
Yes can confirm it crashes with org.eclipse.ui.forms_3.13.700.v20251009-1850.jar but works with org.eclipse.ui.forms_3.13.200.v20240108-1539.jar in the app. All other SWT-related jars were left as the 2025 versions I showed above.

I'll try to make a small reproducible case, if required (not sure if this is a known issue or not).

[ptziegler]

There was a runtime arg that worked once when I tried it (AI told me, but seems to have forgot).

Do you mean osgi.os?

public static void main(String[] args) {
    System.setProperty("osgi.os", "win32");
    System.out.println(Platform.getOS());
}

This unsurprisingly returns win32 and null, if the property is not set, which would then lead to your NPE.

[merks]

I think that folks (often) forget that some things do work standalone and because there are no tests for that, it's easy to use something that doesn't work for such cases. (Just as folks often assume there is always a Workbench.)

[ptziegler]

In any case, I think there are three options:

1. The ExpandableComposite uses SWT.getPlatform() to check the operating system.

2. Platform.getOS() returns OS_UNKNOWN instead of null if the operating system can't be determined (as specified in the JavaDoc).

3. Platform.isWindows() (as well as isLinux() and isMac()) get an explicit null-check.

Edit: It also looks like the problematic code has already been removed again with 94f47d8. So this problem wouldn't occur with the 2026-03.

[jeffecom]

Yes, this test passes for me on forms 2025-12

    @Test
public void swtOsgiPropertyMustBeSet() {
	assertNull(Platform.getOS());
	
	System.setProperty("osgi.os", "win32");
	
	assertEquals("win32", Platform.getOS());
}

Unfortunately, I get all sorts of WindowBuilder errors too. Well, not much in the way of errors: it just fails to display the form. It does show the component tree in some cases. WindowBuilder gives me update anxiety because something always goes wrong. In the past I could change my code to cope with the new requirements, but it fails mysteriously in the latest versions.

I'll raise an issue once I can narrow down what it is. It might be the ByteBuddy stuff because I was overriding isDisposed(). Removing that fixed some problems, but forms design has a problem. Maybe it's related, but surely the Eclipse IDE knows the OS...

Thanks for your help!

[jeffecom]

Thank you all for your amazing help! I'll close the issue.

[akurtakov]

If something is meant to be working in standalone manner - it should be fixed and accompanied by a test so it doesn't regress.

[laeubi]

Regardless of all the interesting details the implementation is wrong. I'll push a fix.