contact import fails when zip code is blank

CRM/Utils/Geocode/ZipTable.php throws an error during contact import when zip code is blank.

I fixed the problem by avoiding the coordinate lookup if zip code is blank:

$zip = addslashes( $values['postal_code'] );
if ( $zip !== '' ) {
$query = 'SELECT latitude, longitude FROM zipcodes WHERE zip = ' . addslashes( $values['postal_code'] );
$dao =& CRM_Core_DAO::executeQuery( $query );
if ( $dao->fetch( ) )

{ $values['geo_code_1'] = $dao->latitude ; $values['geo_code_2'] = $dao->longitude; return true; }

}