Yes you can use coalesce. Example coalesce($field}, 0) This happens because a empty field gets '' empty string then the math fails.
coalesce(value1, value2)
Returns the first nonempty value. This function supports only two values.
coalesce(${question_one}, ${question_two})
Bookmark this page its super handy https://doc.arcgis.com/en/survey123/desktop/create-surveys/xlsformformulas.htm