Ubooquity doesn't open on Windows 10

I've never used Ubooquity before so I've been following the startup guide. I downloaded the .jar file from the website, put it in a folder, double-clicked it and... nothing. It generated a few folders, a JSON file and a database file, but nothing actually opened.

I checked the logs and it said the following (I tried a few more times and it just repeated the same text in my logs):

20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Running with the following parameters - headless: false, libraryport: -1, adminport: -1, remoteadmin: false, host: null, debug: false, execdir: D:\Software\Ubooquity
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - #############################
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - # Starting Ubooquity #
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - #############################
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Java version: 15.0.1
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Java vendor: Oracle Corporation
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - java vm name: Java HotSpot(TM) 64-Bit Server VM
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - java runtime name: Java(TM) SE Runtime Environment
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Max heap size available: 3058 MB
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - OS name: Windows 10
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - OS version: 10.0
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - OS architecture: amd64
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Loading local version info
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Ubooquity 2.1.2 built on 2018-10-14 at 12:58
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Creating application folders
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Loading preferences
20210602 23:38:35 [main] INFO com.ubooquity.Ubooquity - Saving preferences
20210602 23:38:35 [main] INFO org.eclipse.jetty.util.log - Logging initialized @2828ms to org.eclipse.jetty.util.log.Slf4jLog
20210602 23:38:35 [Thread-2] INFO com.ubooquity.b - Stopping internal server...
20210602 23:38:35 [Thread-2] INFO com.ubooquity.data.feeder.a - Aborting content scan...
20210602 23:38:35 [Thread-2] ERROR com.ubooquity.b - Error while stopping internal server
java.lang.NullPointerException: Cannot invoke "org.eclipse.jetty.server.ServerConnector.stop()" because "this.c" is null
at com.ubooquity.d.e.a(SourceFile:99) ~[Ubooquity.jar:2.1.2]
at com.ubooquity.b.c(SourceFile:112) ~[Ubooquity.jar:na]
at com.ubooquity.Ubooquity.C(SourceFile:216) ~[Ubooquity.jar:na]
at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]
20210602 23:38:35 [Thread-2] INFO com.ubooquity.b - Internal server stopped
20210602 23:38:35 [Thread-2] INFO com.ubooquity.Ubooquity - Ubooquity has closed.
20210602 23:38:50 [main] INFO com.ubooquity.Ubooquity - Running with the following parameters - headless: false, libraryport: -1, adminport: -1, remoteadmin: false, host: null, debug: false, execdir: D:\Software\Ubooquity

Is there anything I'm missing out or doing wrong?