/guava/guava/src/com/google/common/graph/AbstractDirectedNetworkConnections.java
this.inEdgeMap = checkNotNull( inEdgeMap) ;checkNotNull( edge) ;
checkNotNull ( edge ) ;
} N previousNode = inEdgeMap.put(edge, node); checkState(previousNode == null); } @Override public void addOutEdge(E edge, N node) { <extra_id_0> checkNotNull(node); N previousNode = outEdgeMap.put(edge, node); checkState(previousNode == null); } }