Android透传消息发送失败

这样发送透传消息失败了，不知是什么原因，请大神指教。
String content; JSONObject jsonObject = new JSONObject(); try { jsonObject.put("type", 2); jsonObject.put("g_id", groupId); jsonObject.put("operation", operation); jsonObject.put("u_name", u_name); jsonObject.put("timestamp", System.currentTimeMillis()); content = jsonObject.toString(); LogUtil.logd("sendGroupMemberChangeCMDMessage>>>content:"+content); EMMessage message = EMMessage.createSendMessage(BLMessage.Type.CMD); EMCmdMessageBody cmdMessageBody = new EMCmdMessageBody(content); message.setChatType(EMMessage.ChatType.GroupChat); message.setTo(groupId); message.addBody(cmdMessageBody); message.setAttribute("isReadThenBurn", isReadThenBurn); sendMessage(message); } catch (JSONException e) { e.printStackTrace(); }
 
报错提示如下：
onErrorjava.lang.NullPointerException: Attempt to invoke virtual method 'com.hyphenate.chat.adapter.EMAConversation com.hyphenate.chat.adapter.EMAChatManager.conversationWithType(java.lang.String, com.hyphenate.chat.adapter.EMAConversation$EMAConversationType, boolean)' on a null object reference