[system admin - groups] fixup for the 'Owner' value in creating new groups (#6561)

frontend/src/components/dialog/sysadmin-dialog/sysadmin-create-group-dialog.js

@@ -38,9 +38,9 @@ class SysAdminCreateGroupDialog extends React.Component {
   };
 
   handleSelectChange = (option) => {
-    // option can be null
+    // option can be `null`, `[{...}]`, or `[]`
     this.setState({
-      ownerEmail: option ? option.email : ''
+      ownerEmail: option && option.length ? option[0].email : ''
     });
   };