**Description**
The documentation and the error message of the [check-migrations](https://airflow.apache.org/docs/apache-airflow/stable/cli-and-env-variables-ref.html#check-migrations) / `def check_migrations` could be more verbose.  This check can fail if the underlying database was never initialised.


**Use case / motivation**

We are deploying our airflow helm chart with terraform helm provider. This provider has a [bug](https://github.com/hashicorp/terraform-provider-helm/issues/683) with helm hook. If airflow would give us a bit more verbose error message why could the `check-migrations` fail, we would find the underlying error/bug much sooner.


**Are you willing to submit a PR?**
Yes



airflow/utils/db.py
"""
    :session: session of the sqlalchemy
    :rtype: list[str]
    """
    errors_ = []
    for check_fn in (check_conn_id_duplicates, check_conn_type_null):
        err = check_fn(session)
        if err:
            errors_.append(err)
    return errors_
def upgradedb():