AtributeError: 'NoneType' object has no attribute 'resume_reading'

• asyncpg version: 0.22.0
• PostgreSQL version: 12
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: Yes
• Python version: 3.8
• Platform: Linux
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?: 3.8?
• Can the issue be reproduced under both asyncio and
  uvloop?: Yes

I saw this issue AtributeError: 'NoneType' object has no attribute 'resume_reading'.
Below is the sample code we use. The version of aiohttp is 3.7.4.post0

from aiohttp.web_response import StreamResponse 
from aiohttp.web_request import Request 
import asyncpg.pool

async def test_get_response(req: Request)
	pool = await asyncpg.create_pool(database='xxx', user='xxx', ....)

	sql = '''
	xxx
	'''
	async with pool.acquire() as db_conn:
	        response = StreamResponse()
	        response.headers.add('Content-Type', 'text/csv; charset=utf-8')
	        await response.prepare(req)
	        await db_conn.copy_from_query(
	            sql,
	            header=True,
	            format='csv',
	            output=response.write
	        )
	        return response

Below is the exception.

File "/root/.local/share/virtualenvs/xxxx/lib/python3.8/site-packages/asyncpg/connection.py", line 784, in copy_from_query
return await self._copy_out(copy_stmt, output, timeout)
File "/root/.local/share/virtualenvs/xxxx/lib/python3.8/site-packages/asyncpg/connection.py", line 989, in _copy_out
return await self._protocol.copy_out(copy_stmt, writer, timeout)
......
File "asyncpg/protocol/protocol.pyx", line 359, in copy_out
File "asyncpg/protocol/protocol.pyx", line 132, in asyncpg.protocol.protocol.BaseProtocol.resume_reading
File "/usr/local/lib/python3.8/asyncio/sslproto.py", line 344, in resume_reading
self._ssl_protocol._transport.resume_reading()
AttributeError: 'NoneType' object has no attribute 'resume_reading'

We don’t have a good repro - someone who knows the code might have a good idea about why it happens?

thanks