Dill TypeError: cannot pickle 'sqlite3.Connection' object. No Sqlite anywhere in function

Question

I am getting TypeError: cannot pickle 'sqlite3.Connection' object when attempting to pickle a function. The thing is, I don't use sqlite anywhere in my project and definitely nowhere in this function.

Here is a minimal working example that shows the error:

    def test_outer(a):
        def test_inner(a):
            return a+1
        return a
    dill.dumps(test_outer)