At the moment [when there are no results returned](https://github.com/ropensci/europepmc/blob/86ccdfc262965d0d46ba0349a744208cc228b4f1/R/epmc_search.r#L105), `md` is set to NULL and the block is closed without setting the `hit_count` attr. It would be good to add to add this line ``` attr(md, "hit_count") <- 0 ``` before exiting