Exception!

exception 'Exception' with message 'Where clause does not take a value of type: NULL' in /home/iowatour/htdocs/classes/db.class.php:443 Stack trace: #0 /home/iowatour/htdocs/classes/db.class.php(275): DB->where_clause(NULL) #1 /home/iowatour/htdocs/city-search/index.php(21): DB->get('citr_cities', NULL) #2 {main}
Line: 443
File: /home/iowatour/htdocs/classes/db.class.php
Backtrace:
#0 /home/iowatour/htdocs/classes/db.class.php(275): DB->where_clause(NULL)
#1 /home/iowatour/htdocs/city-search/index.php(21): DB->get('citr_cities', NULL)
#2 {main}