def __init__(self, tree, filename: str = STDIN) -> None:
self.filename = filename<EOL>
Creates new checker instance.

We only need a filename, since ``eradicate`` has its own logic to read
file contents. And it is unhandy to pass it.
But, without ``tree`` argument ``flake8`` does not call this plugin.

When performance will be an issue - we can refactor it.