node.create, node.set and the other prop appliers map fill/stroke
"none" (either case) and null to an empty fills/strokes list, as
fills: [] already did (undocumented), so an outline-only shape is one
call - agents write "none" for no paint. KEYS and docs/mcp.md
document it; the error names the accepted forms. fill_none_tests
covers create, set, undo, text and the error.