Tree / TreeSelect: no initial selection of node with empty key

[perceptron8]

Describe the bug

Initial selection breaks when node's key is empty string.

Reproducer

https://stackblitz.com/edit/tz94ei-dk7k5x?file=src%2Fapp%2Ftree-controlled-demo.html

PrimeNG version

17.18.11

Steps to reproduce the behavior

See reproducer

Expected behavior

Roots of both trees should be selected.

[perceptron8]

Here's reproducer, just in case if stackblitz.com becomes unavailable:

• tree-controlled-demo.ts:

import { Component } from '@angular/core';
import { TreeSelectModule } from 'primeng/treeselect';

@Component({
    selector: 'tree-controlled-demo',
    templateUrl: './tree-controlled-demo.html',
    standalone: true,
    imports: [TreeSelectModule]
})
export class TreeControlledDemo {
    public root = {key: '', label: '(root)'};
}

• tree-controlled-demo.html:

Same instance (selection works fine):
<p-tree selectionMode="single" [value]="[root]" [selection]="root" />

Same key (selection doesn't work):
<p-tree selectionMode="single" [value]="[root]" [selection]="{key: root.key, label: root.label}"  />
`