Aiopg cursor doesn't return fetchone()

Question

I am stuck into a problem with aiopg. There are a one problem when i async with engine and try to return a result to endpoint in FastApi. Look down below for my db class.

class DBEngine:
    def __init__(self, connection_url: str) -> None:
        self.dsn = connection_url
        self.engine: Optional[Engine] = None

    async def connect(self) -> None:
        self.engine = await create_engine(dsn=self.dsn, maxsize=100)

    @property
    def client(self) -> Engine:
        if self.engine:
            return self.engine
        raise Exception("Not connected to database")

    async def close(self) -> None:
        if self.engine:
            self.engine.close()
            await self.engine.wait_closed()

As you can see there is a property, i use it in a code of method of a model class:

class Products(Base):
    __tablename__ = "products"
    UUID = sa.Column(
        UUID(as_uuid=True),
        primary_key=True,
        default=uuid.uuid4,
        unique=True,
        nullable=False,
    )
    product_name = sa.Column(sa.String())

    @classmethod
    async def create_loan(
            cls,
            *,
            product_name: str
    ) -> "Products":
        query = cls.insert_query(
            product_name=product_name
        )

        async with db_engine.client.acquire() as conn:
            cursor = await conn.execute(query)
            return await cursor.fetchone()

And finally i'll show an endpoint in fastapi:

@routes.post("/api/v1/loans")
async def create_loan(loan: Loan):
    product = await Products.create_loan(product_name=loan.product_name)
    return {"loan_id": product.UUID}

ERROR LOG:

**Traceback**
...
aiopg.sa.exc.ResourceClosedError: This result object does not return rows. It has been closed automatically.

Please tell me what's wrong, i spent so much time to solve this problem. Feel free to answer, thanks.