[cups.general] print jobs on empty files

[gmail]

# cat emptyfile | lp 
lp: stdin is empty, so no job has been sent. 

# ls -l /var/spool/cups/tmp 
total 0 
-rw-------  1 root root 0 Mar  8 10:28 45efd74491a30 

# ls -l /var/tmp 
total 0 

# su testuser

# cat emptyfile | lp 
lp: stdin is empty, so no job has been sent. 

# ls -l /var/tmp 
total 0 
-rw-------  1 frank4 testomg2 0 Mar  8 10:30 45efd79cd2725 

# ls -l /var/spool/cups/tmp 
total 0 
-rw-------  1 root root 0 Mar  8 10:28 45efd74491a30 

Question why does cups create print jobs for empty files ?