Add missing __repr__ to streams.EmptyStreamReader (#6916)

**EmptyStreamReader** currently inherits `__repr__` from
**StreamReader** , which then tries to access non-existing fields,
causing AttributeErrors. The bug causes issues like this in upstream
code: miguelgrinberg/python-socketio#1032

This PR adds a custom `__repr__` to EmptyStreamReader to fix the
problem.

CHANGES/6916.bugfix

@@ -0,0 +1 @@
+Add __repr__ to EmptyStreamReader to avoid AttributeErrors.

CONTRIBUTORS.txt

@@ -161,6 +161,7 @@ Jake Davis
 Jakob Ackermann
 Jakub Wilk
 Jan Buchar
+Jarno Elonen
 Jashandeep Sohi
 Jean-Baptiste Estival
 Jens Steinhauser

aiohttp/streams.py

@@ -494,6 +494,9 @@ class EmptyStreamReader(StreamReader):  # lgtm [py/missing-call-to-init]
     def __init__(self) -> None:
         pass
 
+    def __repr__(self) -> str:
+        return "<%s>" % self.__class__.__name__
+
     def exception(self) -> Optional[BaseException]:
         return None
 

tests/test_streams.py

@@ -1100,6 +1100,7 @@ async def test_unread_empty(self) -> None:
 
 async def test_empty_stream_reader() -> None:
     s = streams.EmptyStreamReader()
+    assert str(s) is not None
     assert s.set_exception(ValueError()) is None
     assert s.exception() is None
     assert s.feed_eof() is None