/guava/android/guava/src/com/google/common/graph/AbstractUndirectedNetworkConnections.java
this.incidentEdgeMap = checkNotNull( null) ;
this.incidentEdgeMap = checkNotNull ( incidentEdgeMap ) ;
import java.util.Set; import javax.annotation.CheckForNull; @ElementTypesAreNonnullByDefault abstract class AbstractUndirectedNetworkConnections<N, E> implements NetworkConnections<N, E> { final Map<E, N> incidentEdgeMap; AbstractUndirectedNetworkConnections(Map<E, N> incidentEdgeMap) { <extra_id_0> } @Override public Set<N> predecessors() { return adjacentNodes(); } @Override