ender man doesn't drop ender pearl when you kill them when you have the thorns enchantment on your armor

 when you have the thorns enchantment on your armor if you kill a ender man you will not get a ender pearl and i tried multiple times and i got the same result.

Expected result : 

the ender man should drop a  ender pearl.

 
Actual result :
the ender man doesn't drop any thing.
 
 how to reproduce : 

1. Get a full enchanted thorns armor.
2. Find 3 to 6 ender man then start killing them in gamemode survival 

 

Finally, I think that this bug should be fixed because it can affect the automatic farms