Server crashed and doesn't let me in again

The server crashed and after that I always get kicked with "Internal server error".

This shows up in the console:

Crashlog: https://hastebin.com/xoqewulizo.sql

[21:10:02] [Server thread/WARN]: Failed to handle packet for /IP java.lang.IllegalStateException: Not a JSON Object: null at com.google.gson.JsonElement.getAsJsonObject(JsonElement.java:90) ~[server.jar:?] at wk.a(SourceFile:82) ~[server.jar:?] at wk.<init>(SourceFile:48) ~[server.jar:?] at vl.a(SourceFile:923) ~[server.jar:?] at tb.<init>(SourceFile:162) ~[server.jar:?] at vl.g(SourceFile:443) ~[server.jar:?] at ua.b(SourceFile:113) ~[server.jar:?] at ua.X_(SourceFile:65) ~[server.jar:?] at hw.a(SourceFile:238) ~[server.jar:?] at tx.c(SourceFile:170) [server.jar:?] at net.minecraft.server.MinecraftServer.w(SourceFile:716) [server.jar:?] at sk.w(SourceFile:357) [server.jar:?] at net.minecraft.server.MinecraftServer.v(SourceFile:623) [server.jar:?] at net.minecraft.server.MinecraftServer.run(SourceFile:525) [server.jar:?] at java.lang.Thread.run(Thread.java:745) [?:1.8.0_25]