@Override
 public boolean canAddSourceContainers(final ISourceLookupDirector director) {
   final ISourceContainer[] containers = director.getSourceContainers();
   for (final ISourceContainer container : containers) {
     if (container.getType().getId().equals(AllRProjectsSourceContainer.TYPE_ID)) {
       return false;
     }
   }
   return true;
 }
 /* (non-Javadoc)
  * @see org.eclipse.debug.internal.core.sourcelookup.ISourceContainerType#getMemento(org.eclipse.debug.internal.core.sourcelookup.ISourceContainer)
  */
 public String getMemento(ISourceContainer container) throws CoreException {
   if (this.equals(container.getType())) {
     return getDelegate().getMemento(container);
   }
   IStatus status =
       new Status(
           IStatus.ERROR,
           DebugPlugin.getUniqueIdentifier(),
           DebugPlugin.ERROR,
           SourceLookupMessages.SourceContainerType_0,
           null);
   throw new CoreException(status);
 }