Mark activity as optional in ConversationParameters (#4873)

Author: ceciliaavila

libraries/botframework-schema/etc/botframework-schema.api.md

@@ -711,7 +711,7 @@ export interface ConversationMembers {
 
 // @public
 export interface ConversationParameters {
-    activity: Activity;
+    activity?: Activity;
     bot: ChannelAccount;
     channelData: any;
     isGroup: boolean;

libraries/botframework-schema/src/index.ts

@@ -873,7 +873,7 @@ export interface ConversationParameters {
      * (Optional) When creating a new conversation, use this activity as the initial message to the
      * conversation
      */
-    activity: Activity;
+    activity?: Activity;
     /**
      * Channel specific payload for creating the conversation
      */