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

If you have previously renamed your connection string in appsettings file and you have omitted to rename it in DesignTimeDbContextFactory class (if you have it in your project) and that is checked by Entity framework, then you may run in this issue.