The break change for relations of ProductService.findOne() on V2.1

[tianyingchun]

Describe the bug
The productService.findOne() can not correct apply customized relations

To Reproduce
Steps to reproduce the behavior:

it seems that there is a break change for productService.findOne()

e.g.

const product = await this.productService.findOne(ctx, productId, [
      'variants',
      'variants.facetValues',
    ]);

above code will return property variants as array
after upgrade V2.1 the relations can. not to apply, the variants return null

Expected behavior
Should correct keep custom relations

Environment (please complete the following information):

• @vendure/core version:2.1
• Nodejs version: 18
• Database (mysql/postgres etc):mysql

Additional context
upgrade V2.1 app is break down.