aiomysql==0.0.20 fetchall() returns empty tuple except empty list

```py3
async def callproc(self, procedure: str, rows: int, values: list = None):
try:
async with self.pool.acquire() as conn:
async with conn.cursor(aiomysql.DictCursor) as cur:
await cur.callproc(procedure, [*values])
result = None
if rows == 1:
result = await cur.fetchone()
# elif rows > 1:
# result = await cur.fetchmany(rows)
elif rows == -1:
result = await cur.fetchall()
elif rows == 0:
pass
await cur.close()
return result
```

Expected result of execution None or empty list, but I receive an empty tuple.