Cuando utilizo el comando Add-Migration de la migración de Entity Framework, obtengo la siguiente excepción:

System.NullReferenceException: Object reference not set to an instance of an object. at System.Data.Entity.Migrations.Extensions.ProjectExtensions.GetFileName(Project project, String projectItemName) at System.Data.Entity.Migrations.MigrationsCommands..ctor(Object project, Object startUpProject, String configurationTypeName, String connectionStringName, String connectionString, String connectionProviderName, PSCmdlet cmdlet)

¿Alguna idea?