private final Deque<Iterator<T>> stack;

    PreOrderIterator(T root) {
      this.stack = new ArrayDeque<>();
      stack.addLast(singletonIterator(checkNotNull(root)));
    }

    @Override
    public boolean hasNext() {
      return !stack.isEmpty();
    }

    @Override
    public T next() {
      Iterator<T> itr = stack.getLast(); // throws NSEE if empty

    // TODO: verify contents afterward
    // TODO: something shiny and new instead of Stack
    // TODO: test whether null is supported (create a Feature)
    /**
     * The elements to be returned by future calls to {@code next()}, with the first at the top of
     * the stack.
     */
    final Stack<E> nextElements = new Stack<>();

    /**

     *
     * @param content
     * @param error
     */
    void debug(CharSequence content, Throwable error);

    /**
     * Send an exception to the user in the <b>debug</b> error level.<br>
     * The stack trace for this exception will be output when this error level is enabled.
     *
     * @param error
     */
    void debug(Throwable error);

    /**
     * @return true if the <b>info</b> error level is enabled

    // TODO: verify contents afterward
    // TODO: something shiny and new instead of Stack
    // TODO: test whether null is supported (create a Feature)
    /**
     * The elements to be returned by future calls to {@code next()}, with the first at the top of
     * the stack.
     */
    final Stack<E> nextElements = new Stack<>();

    /**

                stack.push(list);
            }

            list.add(parseItem(isCombination, isDigit, version.substring(startIndex)));
        }

        while (!stack.isEmpty()) {
            list = (ListItem) stack.pop();
            list.normalize();
        }
    }

    private static Item parseItem(boolean isDigit, String buf) {
        return parseItem(false, isDigit, buf);
    }

     * setException(stackOverflowError) would fail:
     *
     * - If the stack overflowed before set()/setValue() could even store the result in the output
     * Future, then a call setException() would likely also overflow.
     *
     * - If the stack overflowed after set()/setValue() stored its result, then a call to
     * setException() will be a no-op because the Future is already done.

  - url: https://www.mongodb.com/developer/languages/python/python-quickstart-fastapi/?utm_campaign=fastapi_framework&utm_source=fastapi_sponsorship&utm_medium=web_referral
    title: Simplify Full Stack Development with FastAPI & MongoDB
    img: https://fastapi.tiangolo.com/img/sponsors/mongodb.png
  - url: https://zuplo.link/fastapi-gh
    title: 'Zuplo: Scale, Protect, Document, and Monetize your FastAPI'

        } else {
            logger.warn("The metadata {} {}{}", metadata, errorType, msg);
        }
    }

    @Override
    public void artifactDescriptorInvalid(RepositoryEvent event) {
        // The exception stack trace is not really interesting here
        logger.warn(
                "The POM for {} is invalid, transitive dependencies (if any) will not be available: {}",
                event.getArtifact(),

    /**
     * Helper class to traverse graph. Required to make the containing method thread-safe
     * and yet use class level data to lessen stack usage in recursion
     */
    private class ClasspathGraphVisitor {
        MetadataGraph graph;

        ClasspathContainer cpc;

        List<MetadataGraphVertex> visited;

// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful