Error: EXC_BAD_ACCESS (code = 2, address = 0x7fff4f6c1f98) in my Tower Defense code

let x: Int

let y: Int

init (x: Int, y: Int) {
    self.x = x
    self.y = y
}

let p1 = Point(x: 0, y:0)

///Returns the surrounding points in range of
///the current one
func points(inRange range: Int = 1) -> [Point] {
    var results = [Point]()
    let lowerBoundOfXRange = x - range
    let upperBoundOfXRange = x + range

    let lowerBoundOfYRange = y - range
    let upperBoundOfYRange = y + range

    for xCoordinate in lowerBoundOfXRange...upperBoundOfXRange {
        for yCoordinate in lowerBoundOfYRange...upperBoundOfYRange {
            let coordinatePoint = Point(x: xCoordinate, y: yCoordinate)
            results.append(coordinatePoint)
        }
    }
    return results
}

class Enemy {
    var life: Int = 2
    let position: Point
    init(x: Int, y: Int) {
        self.position = Point(x: x, y: y)
    }
    func decreaseLife(by factor: Int) {
    life -= factor
    }
}

class SuperEnemy: Enemy {

    let isSuper: Bool = true

    override init(x: Int, y: Int) {
        super.init(x: x, y: y)
        self.life = 50
    }
}

    init (x: Int, y: Int) {
        self.position = Point(x: x, y: y)
    }

func fire(at enemy: Enemy) {
        if isInRange(of: enemy) {
            enemy.decreaseLife(by: strength)
            print("Gotcha!")
        } else {
            print("Darn! Out of Range!")
        }
        }
    func isInRange(of enemy: Enemy) -> Bool {
        let availablePositions = position.points(inRange: range)
        for point in availablePositions {
            if point.x == enemy.position.x && point.y == enemy.position.y {
                return true
            }
        }
        return false
    }
}

override func fire(at enemy: Enemy) {
    while enemy.life >= 0 {
    enemy.decreaseLife(by: strength)
    }
    print("Enemy destroyed!")
}