Must of the time the field vale will be false or NULL if it is empty. You need to check for empty
if(empty(get_field($term_id)) {
this might also work
if (!get_field($term_id)) {
However, this could be a problem if the actual value of the field is something that evaluates to empty but is a valid value, for example an empty string, 0, false, etc. So depending on the type of field you might need to check for different things.
