Currently in NMS exists a validation for avoid make a Item Entity can set a empty ItemStack.

this validation causes inconsistences with loot tables in spawn cases, where for example if you try to spawn a loot table of vanilla for chests you throw a error because the chest has empty itemstacks.

Command used in test. 

Note: the loot its random then not in all cases return the error.

/loot spawn ~ ~ ~ loot minecraft:chests/abandoned_mineshaft 

Expected:

The command spawn all the content of this loot

Currently:

The command throw a error when detect a empty itemstack.