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

For me it was that I had appSettings.json instead of appsettings.json for some reason (not quite sure if VS did that with a newly created project or I had renamed it to that). Once I changed the name, it worked fine.