Handling metadata extraction in repositories without or with empty CFF files

[Aidajafarbigloo]

Hello,

While extracting metadata from repositories without a CFF file, we face error, and the absence of CFF or CodeMeta files complicates metadata extraction. (We tried hermes harvesting in local machine by installing via pip.)

We believe there are two potential solutions to address this issue:

1. A feature that allows the option to toggle on/off specific harvesters like cff/CodeMeta. If no CFF/CodeMeta file is present, the corresponding harvester would be disabled to prevent errors.
2. Change in the behavior of the cff/CodeMeta harvester to return an empty dictionary if no CFF/CodeMeta file or an empty CFF/CodeMeta file is found. This would prevent errors and allow the extraction process to proceed smoothly.

We would be glad to know your suggestions, feedback on these solutions or any alternative ideas about this issue.

[led02]

Related to #238