Null res$body crashes

[trestletech]

#' @get /
function(res){
  browser()
  res$setHeader("Location", "/redir")
  res$status <- 307
#  res$body <- "hi"
  res
}

with the res$body commented out crashes the server since httpuv doesn't know how to serialize a request with no body. We should ensure that all requests have a body.