Q:

C# Picturebox Reset

I am making a simple game and I'm stuck with character rotation. 
I made a simple control with arrow keys but without rotation.
Then I used the RotateFlipType function to get my character rotate but he kept rotating on the same key. So I need to make the picturebox image reset every time a different key is pressed and then rotate it in right direction.
void Rotate(string a)
    {
        switch (a)
        {
            case "up":
                if (rotation != "up")
                {
                    rotation = "up";
                    pb_sprite.ImageLocation = null;
                    pb_sprite.ImageLocation = @"Images/tenk.png";
                }
                break;
            case "down":
                if (rotation != "down")
                {
                    rotation = "down";
                    pb_sprite.ImageLocation = null;
                    pb_sprite.ImageLocation = @"Images/tenk.png";
                    pb_sprite.Image.RotateFlip((RotateFlipType.Rotate180FlipNone));
                }
                break;
        }
    }

The "up" case works fine. But I do get an error when the code comes to rotation. 
System.NullReferenceException

I get it that I removed the location. But I put it back (for resetting the rotation). Why does the compiler still think there is no image?
Thank you.

A:

Try
case "down":
            if (rotation != "down")
            {
                rotation = "down";
                pb_sprite.ImageLocation = null;
                pb_sprite.ImageLocation = @"Images/tenk.png";
                pb_sprite.Load();
                pb_sprite.Image.RotateFlip((RotateFlipType.Rotate180FlipNone));
            }
            break;

