Seems to be an issue with the Drowned mob added in the update. Crash occurred once the weather state changed to rain. Possible conflict within the code?
Environment
Minecraft Version: 18w11a
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 100960240 bytes (96 MB) / 285212672 bytes (272 MB) up to 1073741824 bytes (1024 MB)
JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M
Profiler Position: N/A (disabled)
Player Count: 0 / 8; []
Data Packs: vanilla
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.
#@
Crash report saved to: #@!@# C:\Users\Mervin\AppData\Roaming\.minecraft\crash-reports\crash-2018-03-18_04.38.24-server.txt
<log4j:Event logger="net.minecraft.server.MinecraftServer" timestamp="1521362304911" level="INFO" thread="Client Shutdown Thread">
<log4j:Message><![CDATA[Stopping server]]></log4j:Message>
</log4j:Event>
If the issue is related to the Drowned mob, I'd recommend taking a look at MC-127242