Description

I have tested the latest version from the main branch and encountered a failure with the following code snippet. This issue does not occur with the latest release, so it might be a regression. It is worth investigating before the next release.

from docarray import DocVec, BaseDoc, DocList
from docarray.documents.image import ImageDoc

class Request(BaseDoc):
    images: DocList[ImageDoc]
        
images = DocList[ImageDoc]([ImageDoc(url=f'http://url.com/{i}.png') for i in range(10)])
request = Request(images=images)
request.json()

The code above results in the following error:

ValueError: {'id': '8695291365f8c39b5dc7e5272aff41be', 'url': ImageUrl('http://url.com/0.png', host_type='domain'), 'tensor': None, 'embedding': None, 'bytes_': None} is not a <class 'docarray.documents.image.ImageDoc'>

Steps to reproduce

1. Run the code snippet provided above using the latest version from the main branch.
2. Observe the ValueError.

Expected behavior

The code should run without errors, creating a Request object with a DocList of ImageDoc objects, and output the JSON representation of the request object.

Additional information

The issue does not occur with the latest release. It might be a regression introduced in recent commits.