currently, trailing delimiters in lists are represented by pushing a null item in the list in the parser. Then, some of the usages of lists (but not all of them) are removing the trailing null value from the list before using it.
This breaks when the last value of a list is an explicit null (see #403 for instance, which is caused by calling a variadic function with null as the argument value).

Changes done in nth in 1.5.0 to be more strict about its handling of invalid indexes revealed existing issues with the implementation of lists themselves.