Here 5 options depending on your desired effect.
Set the camera position, so it is centered on a point above the player. (so that there are always enough tiles below the camera to fill the screen.)
Reduce the height of the window to clip the bottom area. (this will require a combination of #1 and reducing the window height to reach the desired effect)
Center the camera at a fixed height, so that the bottom row of tiles is flush with the bottom of the window.
Center the camera on the player, but clamp the height component to a minimum value that shows the bottom row of tiles flush with the bottom of the screen.
Expand the tileset to show tiles farther below the character.
Comment if you need more detail on how to achieve a specific option.