Bad error message when searching in fields that don't exist #295
Description
For example https://spraakbanken4.it.gu.se/karp/v7/query/saldo?q=equals|lemgram|"mor..nn.2"&from=0&size=25&highlight=true
gives 500 and body {"detail": "Internal server error"} because lemgram is not a field in Saldo. Either we should give back zero hits or a message that describes the error.