public List<ExplorerNode> getChildren(final ExplorerNode parent) {
        final K parentKey = getNodeKey(parent);
        final Set<ExplorerNode> children = parentKeyToChildNodesMap.get(parentKey);
        return NullSafe.get(
                children,
                children2 -> children2.stream().toList());
    }
//     * Replaces an existing node with the supplied one. The new node will
//     * be linked to the previous node's parent and children. If the key is
//     * not found an exception will be thrown. Intended for changing other properties
//     * of a node, e.g. the alerts on it.
//     *
//     * MUST be done while under an exclusive lock on this model.
//
stroom-explorer/stroom-explorer-impl/src/main/java/stroom/explorer/impl/AbstractTreeModel.java