anchor.diff:  
     final ResourceProvider? resourceProvider;
   
  -  _PSNode(YamlNode node, this.resourceProvider)
  +  _PSNode(YamlScalar node, this.resourceProvider)
         : text = node.value?.toString(),
           span = node.span;
   
  
positive.code:   }
    return PSEntry(
        _PSNode(key, resourceProvider), _PSNode(value, resourceProvider));
  }
  
  /// Representation of a key/value pair a map from package name to
  
negative.code:   PSEntry? get url;
  }
  
  /// Representation of a leaf-node from `pubspec.yaml`.
  abstract class PSNode {
    Source get source;
    SourceSpan get span;
  
    /// String value of the node, or `null` if value in pubspec.yaml is `null` or
    /// omitted.
    ///
    /// **Example**
    /// ```
    /// name: foo
    /// version:
    /// ```
    /// In the example above the [PSNode] for `foo` will have [text] "foo", and
    /// the [PSNode] for `version` will have not have [text] as `null`, as empty
    /// value or `"null"` is the same in YAML.
    String? get text;
  }
  
  