checkNotNull(nodeToChildrenFunction);
    return new TreeTraverser<T>() {
      @Override
      public Iterable<T> children(T root) {
        return nodeToChildrenFunction.apply(root);
      }
    };
  }

  /** Returns the children of the specified node. Must not contain null. */
  public abstract Iterable<T> children(T root);

  /**

    }

    @BeforeTemplate
    Iterable<N> before2(N root) {
      return new TreeTraverser<N>() {
        @Override
        public Iterable<N> children(N node) {
          return getChildren(node);
        }
      }.preOrderTraversal(root);
    }

    @AfterTemplate
    Iterable<N> after(N root) {

    idx++;

    if (c != '?' && c != ',') {
      while (idx < encodedLen) {
        // Read all the children
        idx += doParseTrieToBuilder(stack, encoded, idx, builder);

        if (encoded.charAt(idx) == '?' || encoded.charAt(idx) == ',') {
          // An extra '?' or ',' after a child node indicates the end of all children of this node.
          idx++;
          break;
        }
      }
    }

    checkNotNull(nodeToChildrenFunction);
    return new TreeTraverser<T>() {
      @Override
      public Iterable<T> children(T root) {
        return nodeToChildrenFunction.apply(root);
      }
    };
  }

  /** Returns the children of the specified node. Must not contain null. */
  public abstract Iterable<T> children(T root);

  /**

    final List<Tree> children;

    public Tree(char value, Tree... children) {
      super(value);
      this.children = Arrays.asList(children);
    }
  }

  private static final TreeTraverser<Tree> ADAPTER =
      new TreeTraverser<Tree>() {
        @Override
        public Iterable<Tree> children(Tree node) {
          return node.children;
        }
      };

    idx++;

    if (c != '?' && c != ',') {
      while (idx < encodedLen) {
        // Read all the children
        idx += doParseTrieToBuilder(stack, encoded, idx, builder);

        if (encoded.charAt(idx) == '?' || encoded.charAt(idx) == ',') {
          // An extra '?' or ',' after a child node indicates the end of all children of this node.
          idx++;
          break;
        }
      }
    }

  }

  private static final TreeTraverser<BinaryNode> VIEWER =
      new TreeTraverser<BinaryNode>() {
        @Override
        public Iterable<BinaryNode> children(BinaryNode root) {
          return Optional.presentInstances(ImmutableList.of(root.left, root.right));
        }
      };

  enum Traversal {
    PRE_ORDER {
      @Override

  <build>
    <resources>
      <resource>
        <directory>..</directory>
        <includes>
          <include>LICENSE</include> <!-- copied from the parent pom because I couldn't figure out a way to make combine.children="append" work -->
          <include>proguard/*</include>
        </includes>
        <targetPath>META-INF</targetPath>
      </resource>
    </resources>
    <plugins>
      <plugin>

  <build>
    <resources>
      <resource>
        <directory>..</directory>
        <includes>
          <include>LICENSE</include> <!-- copied from the parent pom because I couldn't figure out a way to make combine.children="append" work -->
          <include>proguard/*</include>
        </includes>
        <targetPath>META-INF</targetPath>
      </resource>
    </resources>
    <plugins>
      <plugin>

                   JDK6-like APIs.

                   So instead, we use javac9, which doesn't lead to this error.
              -->
              <compilerArgs combine.children="append">
                <arg>-J-Xbootclasspath/p:${settings.localRepository}/com/google/errorprone/javac/${javac.version}/javac-${javac.version}.jar</arg>
              </compilerArgs>
            </configuration>