/guava/guava/src/com/google/common/graph/StandardMutableValueGraph.java
checkNonNegative( edgeCount) ;checkPositive( ++edgeCount) ;
checkPositive ( ++edgeCount ) ;
GraphConnections<N, V> connectionsV = nodeConnections.get(nodeV); if (connectionsV == null) { connectionsV = addNodeInternal(nodeV); } connectionsV.addPredecessor(nodeU, value); if (previousValue == null) { <extra_id_0> } return previousValue; } @Override @CanIgnoreReturnValue @CheckForNull