anchor.diff:      var value = _visit(node.initializer);
       // explicitly initialize to null, to avoid getting `undefined`.
       // TODO(jmesserly): do this only for vars that aren't definitely assigned.
  -    return value != null ? value : new JS.LiteralNull();
  +    return value ?? new JS.LiteralNull();
     }
   
     void _flushLazyFields(List<JS.Statement> body) {
  
positive.code:     var program = <JS.Statement>[
        js.statement("dart_library.library(#, #, #, #, #)", [
          js.string(jsPath, "'"),
          jsDefaultValue != null ? jsDefaultValue : new JS.LiteralNull(),
          js.commentExpression(
              "Imports", new JS.ArrayInitializer(imports, multiline: true)),
          js.commentExpression("Lazy imports",
  
negative.code:   @override
    visitBreakStatement(BreakStatement node) {
      var label = node.label;
      return new JS.Break(label?.name);
    }
  
    @override
    visitContinueStatement(ContinueStatement node) {
      var label = node.label;
      return new JS.Continue(label?.name);
    }
  
    @override
  