anchor.diff:  
       var builder = ChangeBuilder(session: property.resolvedUnit.session);
   
  -    await builder.addDartFileEdit(property.resolvedUnit.path, (builder) {
  +    await builder.addDartFileEdit(property.resolvedUnit.path!, (builder) {
         property._changeCode(builder, (builder) {
           if (leftCode == rightCode && topCode == bottomCode) {
             builder.writeReference(classEdgeInsets);
  
positive.code: 
    /// If this is a `EdgeInsets` typed property, the instance of helper.
    /// Otherwise `null`.
    _EdgeInsetsProperty _edgeInsetsProperty;
  
    PropertyDescription({
      this.parent,
      this.resolvedUnit,
      this.flutter,
      this.classDescription,
      this.instanceCreation,
      this.argumentExpression,
      this.valueExpression,
      this.parameterElement,
      this.protocolProperty,
      this.virtualContainer,
    });
  
  
negative.code: class PropertyDescription {
    static int _nextPropertyId = 0;
  
    final PropertyDescription? parent;
  
    /// The resolved unit, where the property value is.
    final ResolvedUnitResult resolvedUnit;
  
    /// The instance of [Flutter] support for the [resolvedUnit].
    final Flutter? flutter;
  
    /// If the object that has this property is not materialized yet, so the
    /// [instanceCreation] is `null`, the description of the object to
    /// materialize.
    final ClassDescription? classDescription;
  
    /// The instance creation of the object that has this property. Or `null`
    /// if the object is not materialized yet, in this case [classDescription]
    /// is set.
    final InstanceCreationExpression? instanceCreation;
  
    /// Information about the `Container` property, which is not based on an
    /// actual [instanceCreation] of the `Container` widget, i.e. is not
    /// materialized.
    final VirtualContainerProperty? virtualContainer;
  
    /// If the property is set, the full argument expression, might be a
    /// [NamedExpression].
    final Expression? argumentExpression;
  
    /// If the property is set, the value part of the argument expression,
    /// the same as [argumentExpression] if a positional argument, or the
    /// expression part of the [NamedExpression].
    final Expression? valueExpression;
  
    /// The parameter element in the object constructor that is actually
    /// invoked by [instanceCreation], or will be invoked when
    /// [classDescription] is materialized.
    final ParameterElement? parameterElement;
  
    /// Optional nested properties.
    final List<PropertyDescription> children = [];
  