Null Reference exception when adding empty channel in MS Teams

[VKAlwaysWin]

Name: Issues for IsStartActivity. Example:
https://github.com/microsoft/botframework-solutions/blob/124b9a1c108e1ce854603fb397b411d7d8f30d88/lib/csharp/microsoft.bot.builder.solutions/microsoft.bot.builder.solutions/Extensions/ActivityEx.cs

Language: C#

Description

MembersAdded can be null with ActivityTypes.ConversationUpdate

To Reproduce

1.Install bot to ms teams
2.Use IsActivity extension. For example: turnContext.Activity.IsStartActivity()
3. Create new empty channel.

Expected behavior

No error is thrown.

Screenshots

Additional context

Fix can be something like:
if (activity.MembersAdded != null && activity.MembersAdded.Any(m => m.Id == activity.Recipient.Id)) for IsStartActivity method