Fix strict type errors #22

	name: beets-oldestdate

	on: [push, pull_request]

	jobs:
	build:

	runs-on: ubuntu-latest
	strategy:
	matrix:
	python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]

	steps:
	- uses: actions/checkout@v3
	- name: Set up Python ${{ matrix.python-version }}
	uses: actions/setup-python@v4
	with:
	python-version: ${{ matrix.python-version }}
	cache: 'pip'
	- name: Install package and dependencies
	run: \|
	python -m pip install --upgrade pip
	pip install flake8 mypy types-python-dateutil
	pip install .
	- name: Lint with flake8
	run: \|
	# stop the build if there are Python syntax errors or undefined names
	flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
	# exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
	flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
	- name: Type checking with mypy
	run: mypy --ignore-missing-imports --strict beetsplug
	- name: Test with unittest
	run: python -m unittest discover -s tests

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