fuse-wiiu doesn't "like" mountpath, no matter if it exists or not

[mariomadproductions]

I'm using the latest commit (89d15fb) on Linux Mint 20.1 (Ubuntu 20.04 based)
Command: java -Dfile.encoding=UTF-8 -jar /home/user/opt/fuse-wiiu/fuse-wiiu.jar -in "Super Mario 3D World (USA) (En,Fr,Es)/" -mountpath "/home/user/mnt/Super Mario 3D World (USA) (En,Fr,Es)"

Output if mountpath exists:

Mounting to /home/user/mnt/Super Mario 3D World (USA) (En,Fr,Es) is not possible. It's already mounted or in use

Output if mountpath does not exist:

retail common key is okay
WARNING: Dev common key is not as expected
disc key path is: /home/user/.wiiu/discKeys
title key path is: /home/user/.wiiu/titleKeys
Mounting /media/user/data/game/rom/wu_d/Super Mario 3D World (USA) (En,Fr,Es)
Mounting /media/user/data/game/rom/wu_d/Super Mario 3D World (USA) (En,Fr,Es) to /home/user/mnt/Super Mario 3D World (USA) (En,Fr,Es)
fuse: bad mount point `/home/user/mnt/Super Mario 3D World (USA) (En,Fr,Es)': No such file or directory
Exception in thread "main" ru.serce.jnrfuse.FuseException: Unable to mount FS
	at ru.serce.jnrfuse.AbstractFuseFS.mount(AbstractFuseFS.java:281)
	at ru.serce.jnrfuse.Mountable.mount(Mountable.java:20)
	at de.mas.wiiu.jnus.fuse_wiiu.Main.main(Main.java:173)
Caused by: ru.serce.jnrfuse.FuseException: Unable to mount FS, return code = 1
	at ru.serce.jnrfuse.AbstractFuseFS.mount(AbstractFuseFS.java:277)
	... 2 more

Content of the Super Mario 3D World (USA) (En,Fr,Es) input directory:

00000002.app
00000004.app
00000005.app
00000006.app
00000007.app
00000008.app
00000009.app
0000000a.app
0000000c.app
0000000d.app
0000000e.app
0000000f.app
00000010.app
0005000010145d00.key
tmd.app

Same result if I change the file naming to the *.app / title.tmd style.