Bug 49182 What should canceling setRawClasspath do ?
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/VariableBlock.java
String[] entries= JavaCore.getClasspathVariableNames();
		ArrayList elements= new ArrayList(entries.length);
		for (int i= 0; i < entries.length; i++) {
			String name= entries[i];
			CPVariableElement elem;
			IPath entryPath= JavaCore.getClasspathVariable(name);
			if (entryPath != null) {
				elem= new CPVariableElement(name, entryPath, reserved.contains(name));
				elements.add(elem);
				if (name.equals(initSelection)) {
					initSelectedElement= elem;
				}
			} else {				
				JavaPlugin.logErrorMessage("VariableBlock: Classpath variable with null value: " + name); 
			}
		}
		
		fVariablesList.setElements(elements);
		
		if (initSelectedElement != null) {
			ISelection sel= new StructuredSelection(initSelectedElement);
			fVariablesList.selectElements(sel);
		} else {
			fVariablesList.selectFirstElement();
		}
		
		fHasChanges= false;
	}
}