Status: IN
NullIterator is a direct consequence of Composite's transparency choice propagating to Iterator infrastructure: because Composite treats leaves uniformly with composites, leaves must provide iterators even though they have no children, requiring NullIterator as a degenerate always-done implementation — demonstrating that pattern design decisions have transitive costs across pattern boundaries.
Composite's transparency decision creates infrastructure obligations in Iterator, showing design costs propagate across patterns
Depends on (SL): null-iterator-always-done, null-iterator-for-leaf-glyphs, composite-transparency-vs-safety-tradeoff