These old exceptions have a fair amount of overlap given how/where they are being used, which is likely because they were introduced at different points in time, hence we can shorten and simplify the code by replacing them with a more general `ResponseException` instead.
Besides an error message, the new `ResponseException` instances also include:
- A numeric `status` field containing the server response status, similar to the old `UnexpectedResponseException`.
- A boolean `missing` field, to allow easily detecting the situations where `MissingPDFException` was previously thrown.
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