As error says, your object is not initialised before getting used. So debug it, you'll get the cause.
and also you list population code of list is not complete. I have done like this.
lstEmployees.DataSource = employess;
lstEmployees.DataTextField = "Name";
lstEmployees.DataValueField = "Id";
lstEmployees.DataBind();
Here employees is a list containing employee objects and Name and Id are the property of the Employee class