fn.emptyfn.emptyfnempty/apidoc/8.0/fn:empty.xml
If the value of $arg is the empty sequence, the function returns true;
otherwise, the function returns false.
A sequence to test.
If you pass in a single value,
it is treated as a ValueIterator with that single item; therefore, if you
pass in an array, the array is treated as a single value (not as one value
for each item in the array). If you mean to pass in
the values of each item in the array, then you can call
xdmp.arrayValues on the array. argValueIteratorBoolean