you need to initialize the list in client side
AuditTrail auditclass = new AuditTrail();
auditclass.MyObjectVariableList = new object[7];
or in service class constructor initialize the property value
public class AuditTrail
{
private object[] _myObjectVariableList;
public object[] MyObjectVariableList
{
get { return _myObjectVariableList; }
set { _myObjectVariableList = value; }
}
public AuditTrail()
{
MyObjectVariableList= new object[7];
}
}