createUnknownNode method
Create an UnknownNode and add it to the receiver's collection of nodes.
Implementation
ZwNode createUnknownNode(int nodeId) {
if (existingNodeWithId(nodeId) != null) throw 'node $nodeId already exists';
logger.config('creating unknown node $nodeId');
ZwNode node = UnknownNode(nodeId);
add(node);
return node;
}