@CanIgnoreReturnValue
  private NetworkConnections<N, E> addNodeInternal(N node) {
    NetworkConnections<N, E> connections = newConnections();
    checkState(nodeConnections.put(node, connections) == null);
    return connections;
  }
@CanIgnoreReturnValue
  private NetworkConnections<N, E> addNodeInternal(N node) {
    NetworkConnections<N, E> connections = newConnections();
    checkState(nodeConnections.put(node, connections) == null);
    return connections;
  }
@ CanIgnoreReturnValue private NetworkConnections < N , E > addNodeInternal ( N node ) { NetworkConnections < N , E > connections = newConnections ( ) ; checkState ( nodeConnections . put ( node , connections ) == null ) ; return connections ; }
Adds {@code node} to the graph and returns the associated {@link NetworkConnections}.

@throws IllegalStateException if {@code node} is already present
Adds { @code node } to the graph and returns the associated { @link NetworkConnections } .