local get_tiles = function()
  local mask = game.tile_prototypes["transport-drone-road"].collision_mask
  local tiles = {}
  for name, tile in pairs (game.tile_prototypes) do
    local tile_mask = tile.collision_mask
 if tile_mask ~= nil then -- added to fix crash
    if table_size(tile_mask) == table_size(mask) then
      local good = true
      for layer, bool in pairs (mask) do
        if not tile_mask[layer] then
          good = false
          break
        end
      end
      if good then
        table.insert(tiles, name)
      end
    end
 end -- added to fix crash
  end
  return tiles
end