This should now be fixed. See /u/Jayfresh_Respawn's comment here.
Short description: Energy weapons have no magazine slot to see what mag you have, or if you have one.
Steps to reproduce: Pick up an energy weapon, look at the attachment slots in your inventory.
Platform: All Platforms
Expected result (what is meant to happen): There should be an attachment slot that shows what magazine you have.
Actual result (What actually happens): There is no attachment slot to show what magazine you have.
Edited to specify this is all platforms, not just Xbox One.