Inserts an Element
into the array at the specified position.
If the index equals the number of items in the array then the
Element is appended to
Most ArrayElements cannot hold null
values in a meaningful way. So in general, if you provide a null
value this will result in an exception being raised.
Occasionally it is appropriate for ArrayElements to hold null values represented
as NullAtoms. You can indicate this is acceptable, by setting the