Bug 50022 [DND] NPE in DelegatingDragAdapter
DelegatingDragAdapater defines a list "activeListeners" but initializes it only in DragStart. However, the list is referenced in removeDragSourceListener without a null check, thus causing a null pointer exception if no dragStart ever occured.
bundles/org.eclipse.jface/src/org/eclipse/jface/util/DelegatingDragAdapter.java
*			}
 *			public void dragFinished(DragSourceEvent event) {
 *				// no clean-up required
 *			}
 *		});
 *		dragAdapter.addDragSourceListener(new TransferDragSourceListener() {
 *			public Transfer getTransfer() {
 *				return FileTransfer.getInstance();
 *			}
 *			public void dragStart(DragSourceEvent event) {
 *				// enable drag listener if there is a viewer selection
 *				event.doit = !viewer.getSelection().isEmpty();
 *			}
 *			public void dragSetData(DragSourceEvent event) {
 *				File file1 = new File("C:/temp/file1");
 *				File file2 = new File("C:/temp/file2");
 *				event.data = new String[] {file1.getAbsolutePath(), file2.getAbsolutePath()};
 *			}
 *			public void dragFinished(DragSourceEvent event) {
 *				// no clean-up required
 *			}
 *		});
 *		viewer.addDragSupport(DND.DROP_COPY | DND.DROP_MOVE, dragAdapter.getTransfers(), dragAdapter);
 * </pre></code>
 * <p>
 * NOTE: This API is experimental and subject to change including removal.
 * </p>
 * @since 2.2
 */
public class DelegatingDragAdapter implements DragSourceListener {