Setting a foreign key as a nullable key in model file is not working in loopback 4

Describe the bug

I want to set up a field that is defined as a foreign key, but also supports the ability to be null. In the model file, I have this already

  @belongsTo(() => Bill, { keyTo: 'BillID', name: 'Bill' })
  BillID: Number;

But what I want to do is something like this

  @property({
    type: Number,
    required: false,
    jsonSchema: { nullable: true },
    mssql: { "columnName": "BillID", "dataType": "int", "dataPrecision": null, "dataScale": null, "nullable": "YES" },
  })
  @belongsTo(() => Bill, { keyTo: 'BillID', name: 'Bill' })
  BillID: Number;

but that does not work. How can I set this up?

Logs

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Additional information

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Reproduction

not needed as problem is obvious

この issue では、BillID の @property および @belongsTo 宣言を含むモデルファイルを特定しています。まず、LoopBack 4 が nullable な外部キーをどのように表現するかを追跡してください。対応が完了した状態とは、サポートされている構成を確認するか、framework の変更点を明確にし、nullable な BillID の動作を検証できた状態です。