getData bugfix and onDependencyChanged feature

[stutteringp0et]

getData bombs out on an item list with empty elements. I added several tests for "s" before additional tests on properties of "s". This allows dependency changes to continue even on item lists with empty elements.

onDependencyChanged, I passed the source variable from the function input vars to the schema resolver. This allows the resolver to calculate which of an item list is making the modification.