从layerkit ios错误获取消息

我正在通过layer kit iOS SDK创建一个组。组的所有者在创建组时向参与者发送推送消息和一条消息。问题是，当参与者获取消息时，会话对象有时会为空，下面是我的代码

query = [LYRQuery queryWithQueryableClass:[LYRConversation class]];
 query.predicate = [LYRPredicate predicateWithProperty:@"identifier" predicateOperator:LYRPredicateOperatorIsEqualTo value:eventDetail[@"layerConversation"]];
NSError *error = nil;
conversation = [[self.layerClient executeQuery:query error:&error] firstObject];

NSLog(@"%@?????????????????? and layer client  %@",conversation, self.layerClient );