import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import javax.annotation.CheckForNull;

/**
 * Standard implementation of {@link ValueGraph} that supports the options supplied by {@link
 * AbstractGraphBuilder}.
 *
 * <p>This class maintains a map of nodes to {@link GraphConnections}.
 *
 * <p>Collection-returning accessors return unmodifiable views: the view returned will reflect