极光IM JMSGConversation创建消息对象为空

JMSGMessage      *textMessage = nil;
JMSGTextContent *textContent   = [[JMSGTextContent alloc] initWithText:@"你好！"];
textMessage                                 = [self.conversation createMessageWithContent:textContent];

NSLog(@"text --- %@",((JMSGTextContent *)textMessage.content).text);

打印出的text为空，是什么原因？