User name: First or last name empty instead of "unefined"

If a first or last name is not defined during LDAP/AD user creation,
it is not displayed, instead of showing "undefined"

Change-Id: I8cef34d504c14739ae958caec35754ca83aa8228

jams-react-client/src/views/Users/Users.tsx

@@ -310,7 +310,7 @@ export default function Users() {
                       >
                         <GridItem style={{ minHeight: "50px" }}>
                           <h4 className={classes.cardTitle}>
-                            {`${user.firstName} ${user.lastName}`}
+                            {`${user.firstName ?? ""} ${user.lastName ?? ""}`}
                           </h4>
                         </GridItem>
                         <GridItem>