Update ext/mbstring/mbstring.c

Co-authored-by: Gina Peter Banyard <girgias@php.net>

Author: youkidearitai

ext/mbstring/mbstring.c

@@ -3048,7 +3048,7 @@ static void php_do_mb_trim(INTERNAL_FUNCTION_PARAMETERS, MB_TRIM_MODE mode)
 	ZEND_PARSE_PARAMETERS_START(1, 3)
 		Z_PARAM_STR(str)
 		Z_PARAM_OPTIONAL
-		Z_PARAM_STR_OR_NULL(what)
+		Z_PARAM_STR(what)
 		Z_PARAM_STR_OR_NULL(encoding)
 	ZEND_PARSE_PARAMETERS_END();