anchor.diff:  
     @override
     DecoratedType visitIfElement(IfElement node) {
  -    _handleAssignment(node.condition, destinationType: _notNullType);
  +    _handleAssignment(node.condition, destinationType: _nonNullableBoolType);
       NullabilityNode trueGuard;
       NullabilityNode falseGuard;
       if (identical(_conditionInfo?.condition, node.condition)) {
  
positive.code: 
    @override
    DecoratedType visitAssertStatement(AssertStatement node) {
      _handleAssignment(node.condition, destinationType: _notNullType);
      if (identical(_conditionInfo?.condition, node.condition)) {
        var intentNode = _conditionInfo.trueDemonstratesNonNullIntent;
        if (intentNode != null && _conditionInfo.postDominatingIntent) {
  
negative.code: 
    @override
    DecoratedType visitConditionalExpression(ConditionalExpression node) {
      _handleAssignment(node.condition, destinationType: _nonNullableBoolType);
  
      DecoratedType thenType;
      DecoratedType elseType;
  