Define what constitutes an empty item for a field type.
$item: An item that may or may not be empty.
$field: The field to which $item belongs.
TRUE if $field's type considers $item not to contain any data; FALSE otherwise.
Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.
function hook_field_is_empty($item, $field) {
if (empty($item['value']) && (string) $item['value'] !== '0') {
return TRUE;
}
return FALSE;
}