Custom world error

[Adam1609]

• Issue Description: I am just testing to see and it turn out that it has this bug

• Version: v1.6.0beta1

• Server Version: 3.18.0

• Crashdump, backtrace or other files:

• [21:53:57] [Asynchronous Worker #0 thread/CRITICAL]: TypeError: "Return value of pocketmine\level\biome\Biome::getMinElevation() must be of the type int, null returned" (EXCEPTION) in "pmsrc/src/pocketmine/level/biome/Biome" at line 165
  [21:53:57] [Asynchronous Worker #0 thread/CRITICAL]: #0 plugins/MultiWorld/src/czechpmdevs/multiworld/generator/normal/NormalGenerator(187): pocketmine\level\biome\Biome->getMinElevation()
  [21:53:57] [Asynchronous Worker #0 thread/CRITICAL]: Feature #1 pmsrc/src/pocketmine/level/generator/PopulationTask(108): czechpmdevs\multiworld\generator\normal\NormalGenerator->generateChunk(integer 66, integer 48)
  [21:53:57] [Asynchronous Worker #0 thread/CRITICAL]: Feature request: add world editor #2 pmsrc/src/pocketmine/scheduler/AsyncTask(85): pocketmine\level\generator\PopulationTask->onRun()
  [21:53:57] [Asynchronous Worker #0 thread/CRITICAL]: přidej češtinu #3 (): pocketmine\scheduler\AsyncTask->run()
  [21:53:57] [Server thread/CRITICAL]: Could not execute asynchronous task PopulationTask: Task crashed

[MonoAdrian23]

Thousand Times the same Issue.
You can close this, because this issue exist many times.

[Adam1609]

I didn't know this issue is post many times. I just hoped that someone is going to make a pull request to fix this or the owner. This error bug everyone a lot