message: chore(types): make node type optional again
diff: @@ -9,7 +9,7 @@ export type Node<T = any, U extends string | undefined = string | undefined> = {
  id: string;
  position: XYPosition;
  data: T;
  - type: U;
  + type?: U;
  style?: CSSProperties;
  className?: string;
  sourcePosition?: Position;
  