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