TypeError: issubclass() arg 1 must be a class

[Maypher]

First Check

• [X] I added a very descriptive title to this issue.
• [X] I used the GitHub search to find a similar issue and didn't find it.
• [X] I searched the SQLModel documentation, with the integrated search.
• [X] I already searched in Google "How to X in SQLModel" and didn't find any information.
• [X] I already read and followed all the tutorial in the docs and didn't find an answer.
• [X] I already checked if it is not related to SQLModel but to Pydantic.
• [X] I already checked if it is not related to SQLModel but to SQLAlchemy.

Commit to Help

• [X] I commit to help with one of those options 👆

Example Code

from datetime import date
from typing import Optional, Union
from sqlmodel import SQLModel

class Person(SQLModel):
    name: str
    birthdate: Optional[Union[date, str]]
    ....

Description

I want to store information about some people in a MySQL database. Due to the nature of the information, birth dates can be full dates (1940-05-02), month and year (1932-07) or years only (1965). I searched the pydantic documentation and it says to use Unions to accept multiple data types. However, when I try to do this sqlmodel raises the error TypeError: issubclass() arg 1 must be a class. I know the issue comes from union because if I remove it then the code works just fine.

Operating System

Windows

Operating System Details

No response

SQLModel Version

0.0.6

Python Version

3.10.2

Additional Context

No response

[nidico]

Looks like a duplicate of #67, isn't it?