I just performed a pacman update and the following error was encountered...

[2018-06-24 12:49] [ALPM] upgraded lvm2 (2.02.177-1 -> 2.02.178-1)
[2018-06-24 12:49] [ALPM-SCRIPTLET] error: 1 argument(s) specified
[2018-06-24 12:49] [ALPM-SCRIPTLET] 
[2018-06-24 12:49] [ALPM-SCRIPTLET] Usage: vercmp <ver1> <ver2>
[2018-06-24 12:49] [ALPM-SCRIPTLET] /tmp/alpm_mV6qa8/.INSTALL: line 16: [: -lt: unary operator expected
[2018-06-24 12:49] [ALPM] upgraded btrfs-progs (4.16.1-1 -> 4.17-1)

You can ignore the error. It is caused by a depreciated post upgrade script, no longer needed (or used). The install file is removed in git, next build of lvm2 won't have it anymore.