Fix defaults on Redis cache shard config

Author: Fizzadar

synapse/config/redis.py

@@ -35,11 +35,10 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         self.redis_port = redis_config.get("port", 6379)
         self.redis_password = redis_config.get("password")
 
-        cache_shard_config = redis_config.get("cache_shards")
-        if cache_shard_config:
-            self.cache_shard_hosts = cache_shard_config.get("hosts", [])
-            self.cache_shard_expire = cache_shard_config.get("expire_caches", False)
-            self.cache_shard_ttl = cache_shard_config.get("cache_entry_ttl", False)
+        cache_shard_config = redis_config.get("cache_shards", {})
+        self.cache_shard_hosts = cache_shard_config.get("hosts", [])
+        self.cache_shard_expire = cache_shard_config.get("expire_caches", False)
+        self.cache_shard_ttl = cache_shard_config.get("cache_entry_ttl", False)
 
     def generate_config_section(self, **kwargs: Any) -> str:
         return """\