Warning when compiling into native code (dart compile exe)

[tomyeh]

.pub-cache/hosted/pub.dev/html2md-1.3.1/lib/src/converter.dart:111:37: Warning: Operand of null-aware operation '!' has type 'Node' which excludes null.
 - 'Node' is from 'package:html/dom.dart' ('.pub-cache/hosted/pub.dev/html-0.15.4/lib/dom.dart').
    sibling = util.nextSibling(node.node!);