The /usr/share hierarchy is for all read-only architecture-independent data files.
This hierarchy is intended to be shareable among all architecture platforms of a given OS
Note, however, that /usr/share is generally not intended to be shared by different OSes or by different releases of the same OS
Any program or package which contains or requires data that doesn’t need to be modified should store that data in /usr/share. It is recommended that a subdirectory be used in /usr/share for this purpose. Applications using a single file may use /usr/share/misc.
/usr/share/empty is used by the vsftpd to save data.
You can solve this problem by creating the sub-directory empty under /usr/share.
Note: You might need to use sudo as it might show permission denied.