c# entity-framework object reference exception

i have some difficulties with the following exception: "Object reference not set to an instance of an object."

Code-First Migration at EntityFramework MVC5

public class Driver
{   
    [Key]
    public int NumberId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Age { get; set; }

    public string TeamName { get; set; }
    public Team Team { get; set; }

}

the Configuration:

namespace f1app.Migrations.F1app
{
    using Data;
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Migrations;
    using System.Linq;

    internal sealed class Configuration : DbMigrationsConfiguration<f1app.Data.F1appContext>
    {
        public Configuration()
        {
            AutomaticMigrationsEnabled = false;
            MigrationsDirectory = @"Migrations\F1app";
        }

        protected override void Seed(f1app.Data.F1appContext context)
        {

            context.Teams.AddOrUpdate(
                t => t.TeamName, DummyData.getTeams().ToArray());
            context.SaveChanges();

            context.Drivers.AddOrUpdate(
                d => new { d.FirstName, d.LastName }, DummyData.getDrivers(context).ToArray());
        }
    }
}

and the Initial Create:

namespace f1app.Migrations.F1app
{
    using System;
    using System.Data.Entity.Migrations;

    public partial class InitialCreate : DbMigration
    {
        public override void Up()
        {
            CreateTable(
                "dbo.Drivers",
                c => new
                    {
                        NumberId = c.Int(nullable: false, identity: true),
                        FirstName = c.String(),
                        LastName = c.String(),
                        Age = c.String(),
                        TeamName = c.String(maxLength: 30),
                    })
                .PrimaryKey(t => t.NumberId)
                .ForeignKey("dbo.Teams", t => t.TeamName)
                .Index(t => t.TeamName);

            CreateTable(
                "dbo.Teams",
                c => new
                    {
                        TeamName = c.String(nullable: false, maxLength: 30),
                        City = c.String(),
                        Founded = c.String(),
                    })
                .PrimaryKey(t => t.TeamName);

        }

        public override void Down()
        {
            DropForeignKey("dbo.Drivers", "TeamName", "dbo.Teams");
            DropIndex("dbo.Drivers", new[] { "TeamName" });
            DropTable("dbo.Teams");
            DropTable("dbo.Drivers");
        }
    }
}

than get some dummy data for the drivers to get into the table....

public static List<Driver> getDrivers(F1appContext context)
{
    List<Driver> drivers = new List<Driver>(){
        new Driver{
            NumberId=5,
            FirstName="Sebastian",
            LastName="Vettel",
            Age="29",
            TeamName=context.Teams.Find("Ferrari").TeamName,
        },
        new Driver{
            NumberId=44,
            FirstName="Lewis",
            LastName="Hamilton",
            Age="32",
            TeamName= context.Teams.Find("Mercedes").TeamName
        },
        new Driver{
            NumberId=19,
            FirstName="Felipe",
            LastName="Massa",
            Age="36",
            TeamName=context.Teams.Find("Williams").TeamName
        }
    };
    return drivers;
}

and using the PM Console for the Update - update-database -ConfigurationTypeName f1app.Migrations.F1app.Configuration. But only the table for the teams work fine, the Drivers Table doesn't get any data.... Any idea why?