Global list-get operation can inadvertently create list elements

Consider the following sequence of operations:

1. :list-clear(name=attribute)
2. :list-get(name=attribute, index=0)
3. :list-add(name=attribute, value=test)
4. :list-get(name=attribute, index=0)

#2 will return <undefined> as expected. The expected result of #4 is "test". However, it returns <undefined>. This is because #2 will create the missing element at index 0 causing #3 to operate on index 1.