GetParent() return undefined

Questions
1

Hi

I try to work out the below thing

constructor() {
        super();
           this.consumeContext(UMB_DOCUMENT_WORKSPACE_CONTEXT, (instance) => {
                if (!instance)
                    return;
                this.#workspaceContext = instance;
                console.log('Get unique from document :', instance.getUnique());
                console.log('Get parent id from document  :', instance.getParent()?.unique);
            });
           this.consumeContext(UMB_WORKSPACE_CONTEXT, (nodeContext) => {
                const documentContext = nodeContext as UmbDocumentWorkspaceContext;
                console.log('Get unique from work space : ',  documentContext.getUnique());
                console.log('Get parent unique from work space : ',  documentContext.getParentUnique());
            }
}

The result it can return unqiue id from current document, but it always return null on parent unqiue
do you have any idea about this?