Bug 120544 [build path] Editing external source folder does not persist
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceContainerWorkbookPage.java
private void removeEntry() {
		List selElements= fFoldersList.getSelectedElements();
		for (int i= selElements.size() - 1; i >= 0 ; i--) {
			Object elem= selElements.get(i);
			if (elem instanceof CPListElementAttribute) {
				CPListElementAttribute attrib= (CPListElementAttribute) elem;
				String key= attrib.getKey();
				Object value= null;
				if (key.equals(CPListElement.EXCLUSION) || key.equals(CPListElement.INCLUSION)) {
					value= new Path[0];
				}
				attrib.getParent().setAttribute(key, value);
				selElements.remove(i);
			}
		}
		if (selElements.isEmpty()) {
			fFoldersList.refresh();
			fClassPathList.dialogFieldChanged(); 
		} else {
			for (Iterator iter= selElements.iterator(); iter.hasNext();) {
				CPListElement element= (CPListElement)iter.next();
				if (element.getEntryKind() == IClasspathEntry.CPE_SOURCE) {
					List list= ClasspathModifier.removeFilters(element.getPath(), fCurrJProject, fFoldersList.getElements());
					for (Iterator iterator= list.iterator(); iterator.hasNext();) {
						CPListElement modified= (CPListElement)iterator.next();
						fFoldersList.refresh(modified);
						fFoldersList.expandElement(modified, 3);
					}
				}
			}