Why doesnt this work?

This is frustrating me a lot.
“Dereferencing null/undefined value.”

let walls: boolean[][]
for (let x = -1; x < 31; x++) {
    for (let y = -1; y < 31; y++) {
        walls[x][y] = tiles.tileAtLocationIsWall(tiles.getTileLocation(x, y))
    }
}

You’re never assigning anythings to walls. Try this:

let walls: boolean[][] = [];
for (let x = 0; x < 31; x++) {
    walls[x] = [];
    for (let y = 0; y < 31; y++) {
        walls[x][y] = tiles.tileAtLocationIsWall(tiles.getTileLocation(x, y))
    }
}

Lightning quick response! Thanks alot!!