When you summon an enderman with carried:0s, it is treated as if the enderman is holding nothing, however if the enderman is holding nothing the carried tag is not written to the NBT data.
This is pretty inconsistent because if 0s is treated as holding nothing, you would expect it to be saved to NBT if the enderman is holding nothing as well.
In 1.8 versions is possible to test if a enderman don't carries a block
- Summon an enderman holding nothing
- Try to test for carried:0s
→ The command fails