Reproducing on 1.14.21 - Issue has existed for several revisions.
When using the Stop command from the Console, no players are connected, the server crashes on exit.

stop
terminate called after throwing an instance of 'std::bad_variant_access'
what(): Unexpected index
[2020-02-05 22:24:30 INFO] Package: com.mojang.minecraft.dedicatedserver
Version: 1.14.21.0
OS: Linux
Server start: 2020-02-05 22:07:54 PST
Dmp timestamp: 2020-02-05 22:24:30 PST
Upload Date: 2020-02-05 22:24:30 PST
Session ID: c130956d-a20d-45aa-b59a-230c2d912134
Commit hash:
Build id: development
CrashReporter Key: 8c4937c1-64cb-3532-a8dc-1deb28f67293