Bug 30655 [DND] Check selection in NavigatorDragAdapter.dragStart
bundles/org.eclipse.ui.views/src/org/eclipse/ui/views/navigator/NavigatorDragAdapter.java
public void dragSetData(DragSourceEvent event) {
		final int typeMask = IResource.FILE | IResource.FOLDER;
		IResource[] resources = getSelectedResources(typeMask);
		
		if (resources == null || resources.length == 0)
			return;
		
		if (LocalSelectionTransfer.getInstance().isSupportedType(event.dataType)) {
			event.data = LocalSelectionTransfer.getInstance().getSelection();
			return;
		}
		
		if (ResourceTransfer.getInstance().isSupportedType(event.dataType)) {
			event.data = resources;
			return;
		}
		
		if (!FileTransfer.getInstance().isSupportedType(event.dataType))
			return;
		
		final int length = resources.length;
		int actualLength = 0; 
		String[] fileNames = new String[length];
		for (int i = 0; i < length; i++) {
			IPath location = resources[i].getLocation();
			
			if (location != null) 
				fileNames[actualLength++] = location.toOSString();
		}
		if (actualLength == 0)