[MC-143246] Exception when shutting down server if port already in use

1) Start server, and observer no errors

2) Start second server on same port

3) Duplicate port correctly detected

4) However when shutting down server prints NullPointerException

[11:33:10] [main/WARN]: Ambiguity between arguments [teleport, destination] and [teleport, targets] with inputs: [Player, 0123, @e, dd12be42-52a9-4a91-a8a1-11c01849e498]
[11:33:10] [main/WARN]: Ambiguity between arguments [teleport, location] and [teleport, destination] with inputs: [0.1 -0.5 .9, 0 0 0]
[11:33:10] [main/WARN]: Ambiguity between arguments [teleport, location] and [teleport, targets] with inputs: [0.1 -0.5 .9, 0 0 0]
[11:33:10] [main/WARN]: Ambiguity between arguments [teleport, targets] and [teleport, destination] with inputs: [Player, 0123, dd12be42-52a9-4a91-a8a1-11c01849e498]
[11:33:10] [main/WARN]: Ambiguity between arguments [teleport, targets, location] and [teleport, targets, destination] with inputs: [0.1 -0.5 .9, 0 0 0]
[11:33:10] [main/INFO]: Loaded 6 recipes
[11:33:10] [main/INFO]: Loaded 0 advancements
[11:33:10] [Server thread/INFO]: Starting minecraft server version 19w04b
[11:33:10] [Server thread/INFO]: Loading properties
[11:33:10] [Server thread/INFO]: Default game type: SURVIVAL
[11:33:10] [Server thread/INFO]: Generating keypair
[11:33:10] [Server thread/INFO]: Starting Minecraft server on *:25565
[11:33:10] [Server thread/INFO]: Using epoll channel type
[11:33:10] [Server thread/WARN]: **** FAILED TO BIND TO PORT!
[11:33:10] [Server thread/WARN]: The exception was: io.netty.channel.unix.Errors$NativeIoException: bind(..) failed: Address already in use
[11:33:10] [Server thread/WARN]: Perhaps a server is already running on that port?
[11:33:10] [Server thread/INFO]: Stopping server
[11:33:10] [Server thread/INFO]: Saving worlds
[11:33:10] [Server thread/ERROR]: Exception stopping the server
java.lang.NullPointerException: null
	at net.minecraft.server.MinecraftServer.a(SourceFile:554) ~[minecraft_server.19w04b.jar:?]
	at net.minecraft.server.MinecraftServer.h_(SourceFile:582) ~[minecraft_server.19w04b.jar:?]
	at net.minecraft.server.MinecraftServer.run(SourceFile:688) [minecraft_server.19w04b.jar:?]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_191]