getOrAddInput method
Implementation
Node<T> getOrAddInput(T nodeValue) {
if (nodeValue == value) return this;
if (!containsInput(nodeValue)) {
var node = _resolveNode(nodeValue);
return _addInputNode(node) ??
(throw StateError(
"Error adding input node `$nodeValue` to `$value`"));
}
var node = _resolveNode(nodeValue);
assert(_inputs.contains(node));
return node;
}