fix: When chat event type is conversation.chat.completed, a NPE will be thrown;

Error occurred: Cannot invoke "com.coze.openapi.client.connversations.message.model.Message.getType()" because the return value of "com.coze.openapi.client.chat.model.ChatEvent.getMessage()" is null

Author: mifengjun

example/src/main/java/example/chat/StreamChatExample.java

@@ -58,7 +58,8 @@ public static void main(String[] args) {
                 System.out.print(event.getMessage().getContent());
               }
               if (ChatEventType.CONVERSATION_CHAT_COMPLETED.equals(event.getEvent())) {
-                if (MessageType.FOLLOW_UP.equals(event.getMessage().getType())) {
+                if (event.getMessage() != null
+                    && MessageType.FOLLOW_UP.equals(event.getMessage().getType())) {
                   System.out.println(event.getMessage().getContent());
                 } else {
                   System.out.println("Token usage:" + event.getChat().getUsage().getTokenCount());