* @return an <code>EntityFilter</code> that filters out those <code>Target</code>s that
* are not valid choices at the given pipeline position
*/
@Override
public EntityFilter getFilter(TargetActivity activity) {
PipelineActivity previous = pipeline.getPreviousActivity(activity);
while (previous != null) {
EntityFilter filter = getFilter(previous);
if (filter != null) {
return filter;
}