Specifies fields for which the database-defaults should be used.
If you want to force a given field to use the database-defined default, not NULL or undefined, use this method to instruct the database to use default values explicitly. In most cases this will not be necessary unless you are inserting a row that is all default values, as you cannot specify no values in an INSERT query.
Specifying a field both in fields() and in useDefaults() is an error and will not execute.
$fields: An array of values for which to use the default values specified in the table definition.
Drupal\Core\Database\Query\Merge The called object.
public function useDefaults(array $fields) {
$this->defaultFields = $fields;
return $this;
}