Failure to record fields with "0" values

The "event_create_query" function that is used to define the sql query that updates the database currently uses a test of the form

if ($node->$field) {
    $fields[]=$field
    }

in order to identify the fields to modify in the database. But this breaks if the field has been modified to have a value of 0, since then the modified field does not get incorporated. I replaced it with

if (isset($node->$field)) {
    $fields[]=$field
    }

which appears to fix the problem.