I wonder what the Dynamo's behavior is.

Here is from Dynamo's doc:
```
DELETE - If no value is specified, the attribute and its value are removed from the item. The data type of the specified value must match the existing value's data type.

If a set of values is specified, then those values are subtracted from the old set. For example,
if the attribute value was the set [a,b,c] and the DELETE action specified [a,c], then the final
attribute value would be [b]. Specifying an empty set is an error.
```
It seems that it is not specified what will happen if delete all the elements from a set.