in start.sh ensure usename jovyan exists before attempting usermod

base-notebook/start.sh

@@ -30,9 +30,11 @@ done
 # Handle special flags if we're root
 if [ $(id -u) == 0 ] ; then
 
-    # Handle username change. Since this is cheap, do this unconditionally
-    echo "Set username to: $NB_USER"
-    usermod -d /home/$NB_USER -l $NB_USER jovyan
+    # Only attempt to change the jovyan username if it exists
+    if id jovyan &> /dev/null ; then
+        echo "Set username to: $NB_USER"
+        usermod -d /home/$NB_USER -l $NB_USER jovyan
+    fi
 
     # Handle case where provisioned storage does not have the correct permissions by default
     # Ex: default NFS/EFS (no auto-uid/gid)