"Can't remove final physical volume" when vgreduce was issued.

Issue

• I wanted to remove a PV from VG, but I got "Can't remove final physical volume"

[root@server]# vgs
  VG             #PV #LV #SN Attr   VSize   VFree
  server-vg00001   1   0   0 wz--n-  51.07G  51.07G

[root@server]# pvs
  PV              VG             Fmt  Attr PSize   PFree
  /dev/sda4       server-vg00001 lvm2 a-    51.07G  51.07G

[root@server]# vgreduce server-vg00001 /dev/sda4
  Can't remove final physical volume "/dev/sda4" from volume group "server-vg00001"