Fix AttributeError exception when CachedSchemaRegistryClient constructor raises a valid exception.

Author: edenhill

CHANGELOG.md

@@ -15,6 +15,8 @@ v1.8.2 is a maintenance release with the following fixes and enhancements:
  - Fix crash in header parsing (Armin Ronacher, #1165)
  - Added long package description in setuptools (Bowrna, #1172).
  - Documentation fixes by Aviram Hassan and Ryan Slominski.
+ - Don't raise AttributeError exception when CachedSchemaRegistryClient
+   constructor raises a valid exception.
 
 confluent-kafka-python is based on librdkafka v1.8.2, see the
 [librdkafka release notes](https://github.com/edenhill/librdkafka/releases/tag/v1.8.2)

src/confluent_kafka/avro/cached_schema_registry_client.py

@@ -125,7 +125,9 @@ def __exit__(self, *args):
         self.close()
 
     def close(self):
-        self._session.close()
+        # Constructor exceptions may occur prior to _session being set.
+        if hasattr(self, '_session'):
+            self._session.close()
 
     @staticmethod
     def _configure_basic_auth(url, conf):