Object reference not set to an instance of an object

I got error say this line have problem:<b>price = (decimal) cmd.ExecuteScalar(); </b>
I supporse will get one result back.
<b>Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. </b>

public decimal LMQuery(string vehicleCatID,string postCode,string suburb,string state,string city)
        {
            string CS = ConfigurationManager.ConnectionStrings["DBLM3"].ConnectionString;
            using (SqlConnection con = new SqlConnection(CS))
            {
                decimal price = decimal.Zero;
                
                string sqlQuery = string.Empty;

                sqlQuery = "my query is running correct in sql server management";


                SqlCommand cmd = new SqlCommand(sqlQuery,con);

                con.Open();
                price = (decimal) cmd.ExecuteScalar();
                
                return price;             

            }
        }