sugarcrm warning message

I created a new module. When i save a new entry, sugarcrm will show this message:
Warning: preg_match() expects parameter 2 to be string, array given in /var/www/crm/include/utils.php on line 1715

Call Stack
# Time Memory Function Location
1 0.0000 72612 {main}( ) ../index.php:0
2 0.0001 73516 require_once( '/var/www/crm/include/entryPoint.php' ) ../index.php:38
3 0.0019 214344 clean_incoming_data( ) ../entryPoint.php:124
4 0.0067 235068 clean_string( ) ../utils.php:1797
5 0.0068 235120 preg_match ( )
../utils.php:1715

So I traced the code back to line 1797 in utils.php, and found this code "if (isset($_REQUEST['language'])) clean_string($_REQUEST['language']);".

Actually in this new module, i created a field called 'language' and it is MultiSelect type, which is an array. After i change the field name, this warning message disappeared.