Deleting old departments in ServiceDeskPlus

Deleting old departments in ServiceDeskPlus

I am trying to run the query 
update resourceowner set deptid= null where deptid=309; 
but am getting a java error.
java.lang.StringIndexOutOfBoundsException: String index out of range: -1
 at java.lang.String.substring(String.java:1967)

I know what the department IDs are having run another query I got from another post on here, but whichever ID I try I get this error.

What am I missing ?

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