asp.net core 2.0 - Value cannot be null. Parameter name: connectionString

Question

I had the following error in package manager console when Add-Migration

Value cannot be null. Parameter name: connectionString

Answer 1

I had the same problem, because I was using the default value in Startup.cs. I just edited Configuration property from:

public IConfiguration Configuration { get; }

to:

public IConfiguration Configuration;

and it worked! If someone say why would be appreciated.