code: public Node findNode(final String identifier, final boolean recursive) {
  
          Optional<Node> toReturn = getNodes().stream().filter(c -> c.getId().equals(identifier)).findFirst();
          if (!toReturn.isPresent() && recursive && getSubgraphs() != null && !getSubgraphs().isEmpty()) {
  
              // Does the Node with the given identifier exist in any Subgraph?
              toReturn = getSubgraphs().stream()
                      .map(c -> c.getStatements().findNode(identifier, true))
                      .filter(c -> c != null)
                      .findFirst();
          }
  
          // All Done.
          return toReturn.orElse(null);
      }
docs: Finds the Node with the supplied identifier within this Statements (and within any contained Subgraphs, if the
  {@code recursive} flag is true).
  
  @param identifier The identifier to match against the {@link Node#getId()} of a matching Node.
  @param recursive  If {@code true}, the search should recurse into the Statements of Subgraphs.
  @return The Node with the supplied identifier - or null if none was found.