Extend checksum expression to optionally produce warning or error if checksum value is for an empty message

The cryptographic hash functions will each produce a consistent hash value when presented with an empty file (or any empty message). This value is different for each hash function, but a given funtion will always produce the same checksum for an empty message.

For the case where we are receiving digitised files a checksum indicating the file is empty would be considered an error, for born digital, it may be admissible, but it would probably be useful for the Digital Preservation to be given the files as a list of warnings to see if there is any case for including the empty files in the accession, of if they should be dropped as not being a record.

digital-preservation / csv-validator

Extend checksum expression to optionally produce warning or error if checksum value is for an empty message #49