Symptoms
I have simple SQL stored procedure smartobject which is giving error "Nullable Object must have value"
Diagnoses
Issue was relate to SQL unsupported data type.
Resolution
See the link below for help with supported data types.
http://help.k2.com/onlinehelp/k2blackpearl/userguide/4.6.9/webframe.html_ws_sql_01.html
