anchor.diff:        final Map<String, List<int>> locationsJson = <String, List<int>>{};
         for (final _LocationCount entry in newLocations) {
           final _Location location = entry.location;
  -        final List<int> jsonForFile = locationsJson.putIfAbsent(
  -          location.file,
  -          () => <int>[],
  -        );
  -        jsonForFile..add(entry.id)..add(location.line)..add(location.column);
  +        if (location.file != null) {
  +          final List<int> jsonForFile = locationsJson.putIfAbsent(
  +            location.file!,
  +            () => <int>[],
  +          );
  +          jsonForFile..add(entry.id)..add(location.line)..add(location.column);
  +        }
         }
         json['newLocations'] = locationsJson;
       }
  
positive.code:     if (name != null) {
        parts.add(name!);
      }
      parts.add(file);
      parts..add('$line')..add('$column');
      return parts.join(':');
    }
  
negative.code:   });
  
    /// File path of the location.
    final String? file;
  
    /// 1-based line number.
    final int line;
  