Check if the field is empty, if it is then use another field(s) value or even a default value.
Rewrite plugin has the flexibility to use multiple replacement patters, custom string, or a mix of both. But it was lacking the conditional to do the rewrite only if the field values is empty or it is not present in the source.
Needs work
1.0
Plugins
The change is currently missing an automated test that fails when run with the original code, and succeeds when the bug has been fixed.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Please include this in a Drupal 10 release!
@kopeboy see #20. Still needs tests. If someone finishes them, this can be reviewed and RTBC'd afterward. Thanks!