Check that children data !== undefined before calling addNS
Check that children data !== undefined before calling addNS

Otherwise svg is broken.
snabbdom/snabbdom,staltz/snabbdom,snabbdom/snabbdom,paldepind/snabbdom,snabbdom/snabbdom,paldepind/snabbdom,snabbdom/snabbdom,staltz/snabbdom,staltz/snabbdom