android 3.1.2,我去当前的conversation中去获取一条消息，报了一个环信的错，有点不明白是什么意思

我通过一个msgId，通过conversation.getMessage(String msgId,boolean true)去获取会话中的这条消息，然后环信包里报了一个错误，不知道这是什么情况才引起的，麻烦帮忙看一下。
java.lang.NullPointerException: Attempt to invoke virtual method 'long com.hyphenate.chat.adapter.message.EMAMessage.timeStamp()' on a null object reference
                                                                           at com.hyphenate.chat.EMMessage.getMsgTime(Unknown Source)
                                                                           at com.hyphenate.chat.EMConversation$MessageCache.addMessage(Unknown Source)
                                                                           at com.hyphenate.chat.EMConversation.getMessage(Unknown Source)