anchor.diff:                return new Stream.fromIterable([image.data]);
               }
             }
  -          return null;
  -        } else {
  -          throw new UnimplementedError();
  -        }
  +        }
  +        return null;
         }
   
         final imageDataStream = _fetchImageData(image);
  
positive.code:           context.addIssue(DataError.imageDataInvalid, args: [e]);
          } on Exception catch (e) {
            // likely IO error
            context.addIssue(IoError.fileNotFound, args: [e]);
          }
          if (imageInfo != null) {
            resourceInfo.mimeType = imageInfo.mimeType;
  
negative.code:         data = await _fetchBuffer(buffer) as Uint8List;
        } on Exception catch (e) {
          // likely IO error
          context.addIssue(IoError.fileNotFound, args: [e], name: URI);
        }
  
        if (data != null) {
  