Steps to replicate the issue (include links if applicable):
- try to create a claim with a property that doesn't exist. For example, on the Beta Wikidata as of right now, this request (in POST and with a fresh token) fails, because there is no P5831 on Beta Wikidata: https://wikidata.beta.wmflabs.org/w/api.php?action=wbcreateclaim&format=json&entity=Q12480&snaktype=value&property=P5831&value=%22itsastring%22&token=fbb1d314c907dc564cff2a46acffc1f6653800da%2B%5C&formatversion=2
What happens?:
The error message is "Could not find an entity with the ID \"$1\"." (sic, with the $1)
This is doubly confusing: first, it is unclear it is the property that doesn't exist, and not the entity (item etc.) passed in the 'entity' parameter. Secondly, the $1 instead of the value in the message makes one suspect the ID in the request was not parsed properly.
What should have happened instead?:
An error message specifically saying "Property P5831 doesn't exist".