diff --git a/lib/shared/sidebar-utils.js b/lib/shared/sidebar-utils.js
--- a/lib/shared/sidebar-utils.js
+++ b/lib/shared/sidebar-utils.js
@@ -44,7 +44,7 @@
 
 type UserIDAndUsername = {
   +id: string,
-  +username: string,
+  +username: ?string,
   ...
 };
 
@@ -68,10 +68,6 @@
   if (userIsMember(parentThreadInfo, sourceMessageInfo.creator.id)) {
     const { id: sourceAuthorID, username: sourceAuthorUsername } =
       sourceMessageInfo.creator;
-    invariant(
-      sourceAuthorUsername,
-      'sourceAuthorUsername should be set in createPendingSidebar',
-    );
     const initialMemberUserInfo = {
       id: sourceAuthorID,
       username: sourceAuthorUsername,
@@ -88,10 +84,6 @@
     const singleOtherUsername = parentThreadInfo.members.find(
       member => member.id === singleOtherUser,
     )?.username;
-    invariant(
-      singleOtherUsername,
-      'singleOtherUsername should be set in createPendingSidebar',
-    );
     const singleOtherUserInfo = {
       id: singleOtherUser,
       username: singleOtherUsername,
diff --git a/lib/shared/thread-utils.js b/lib/shared/thread-utils.js
--- a/lib/shared/thread-utils.js
+++ b/lib/shared/thread-utils.js
@@ -427,7 +427,7 @@
 
 type UserIDAndUsername = {
   +id: string,
-  +username: string,
+  +username: ?string,
   ...
 };
 type CreatePendingThreadArgs = {
@@ -575,7 +575,7 @@
 function createPendingPersonalThread(
   loggedInUserInfo: LoggedInUserInfo,
   userID: string,
-  username: string,
+  username: ?string,
 ): PendingPersonalThread {
   const pendingPersonalThreadUserInfo = {
     id: userID,