Identify the bug in this token refresh function snippet:

Identify the bug in this token refresh function snippet:

def refresh_token(request):
    token = request.get('refresh_token')
    if token is None:
        return {'error': 'No token provided'}, 400
    if token == 'valid':
        return {'access_token': 'new_token'}, 200
    else:
        return {'error': 'Invalid token'}, 401

# Called with request = {'refresh_token': 'valid_token'}