flask errorhandler wont catch errors if view function returns an invalid response

I want to catch all errors and return an error in json format for my api project.

This is my error handler:

@app.errorhandler(Exception)
def handle_exception(e):
    if not isinstance(e, HTTPException):
        print(e)
        return {
            "code": 500,
            "name": "Internal Server Error",
            "description": repr(e),
        }, 500
    else:
        response = e.get_response()
        response.data = json.dumps({
            "code": e.code,
            "name": e.name,
            "description": e.description,
        })
        response.content_type = "application/json"
        return response

My errorhandler is catching exceptions if it happens inside the view function:

@api.get("/")
def all(user):
    a.b
    return []

This successfully catchs the following exception and return a json response:

name ‘a’ is not defined

But it is not catching if view function is fine but the return value is not json-friendly:

@api.get("/")
def all(user):
    return 1

It raises the folloing error and returns an error in html format.

TypeError: The view function did not return a valid response. The return type must be a string, dict, list, tuple with headers or status, Response instance, or WSGI callable, but it was a int.