Find method.

        Args:
            package (str): package to find.
            **kwargs (): additional keyword arguments.

        Returns:
            PackageSpec: the PackageSpec corresponding to the package, or None.

def find(self, package, **kwargs):
        """
        Find method.

        Args:
            package (str): package to find.
            **kwargs (): additional keyword arguments.

        Returns:
            PackageSpec: the PackageSpec corresponding to the package, or None.
        """
        spec = find_spec(package)
        if spec is None:
            return None
        limit = []
        if '.' in package:
            package, limit = package.split('.', 1)
            limit = [limit]
            spec = find_spec(package)
        if spec is not None:
            if spec.submodule_search_locations:
                path = spec.submodule_search_locations[0]
            elif spec.origin and spec.origin != 'built-in':
                path = spec.origin
            else:
                return None
            return PackageSpec(spec.name, path, limit)
        return None