sql table dependency in wcf service get error

i have this project

https://github.com/zhyan-ise/wcf-demo

when i run the project i get this error

System.NullReferenceException: 'Object reference not set to an instance of an object.'

System.Configuration.ConnectionStringSettingsCollection.this[string].get returned null.

here is my table in sql server 

create table Stocks
(
Code varchar(200) null,
Name varchar(200) null,
Price decimal(18,0) null
)