没有消息的时候，无法找到sentTime

pages/im/group/chat.nvue

@@ -53,7 +53,13 @@
         },
         computed: {
             latestMessage() {
-                return this.messages[this.messages.length - 1]
+                if (this.messages.length > 1) {
+                    return this.messages[this.messages.length - 1]
+                } else {
+                    return {
+                        sentTime: 0
+                    }
+                }
             }
         },
         onLoad(e) {

pages/im/private/chat.nvue

@@ -61,8 +61,14 @@
             }
         },
         computed: {
-            latestMessage() {
-                return this.messages[this.messages.length - 1]
+            latestMessage() {
+                if (this.messages.length > 1) {
+                    return this.messages[this.messages.length - 1]
+                } else {
+                    return {
+                        sentTime: 0
+                    }
+                }
             }
         },
         onLoad(e) {
@@ -103,7 +109,7 @@
                 im.getMessageList(
                     this.conversationType,
                     this.targetId,
-                    this.latestMessage.sentTime,
+                    this.latestMessage.sentTime || 0,
                     1,
                     false,
                     (messages) => {