fix: improve error messages for channel retrieval failures in distributor and relay

model/channel_cache.go

@@ -109,9 +109,6 @@ func CacheGetRandomSatisfiedChannel(c *gin.Context, group string, model string,
 			return nil, group, err
 		}
 	}
-	if channel == nil {
-		return nil, group, errors.New("channel not found")
-	}
 	return channel, selectGroup, nil
 }