Fixing JS error (#6813)

* Fixing JS error

* Fixing js error and storing issue

webapp/utils/channel_utils.jsx

@@ -107,7 +107,7 @@ export function sortChannelsByDisplayName(a, b) {
     const aDisplayName = getChannelDisplayName(a);
     const bDisplayName = getChannelDisplayName(b);
 
-    if (aDisplayName !== bDisplayName) {
+    if (aDisplayName !== null && bDisplayName !== null && aDisplayName !== bDisplayName) {
         return aDisplayName.localeCompare(bDisplayName, locale, {numeric: true});
     }
 

webapp/utils/utils.jsx

@@ -1011,7 +1011,7 @@ export function displayUsernameForUser(user) {
         return name;
     }
 
-    return null;
+    return '';
 }
 
 // Converts a file size in bytes into a human-readable string of the form '123MB'.