Capture the result of an R function, errors and warnings in a data frame

I would like to call a function on each element of a list and store the results, warnings and errors in a data frame. I came up with the following solution, which is neither well-tested nor pretty - so I would be interested in a better way.

library(purrr)

myf <- function(a){
  if(a == 1){
    return(a)
  }else if(a == 2){
    warning("a warning")
    return(a)
  }else if(a == 3){
    stop("an error")
  }
}

a = 1:3

safe_and_quiet <- function(fun, ...){
  safe_fun <- quietly(safely(fun))
  out_safe <- safe_fun(...)
  out <- 
    list(
      result = out_safe$result$result,
      error = out_safe$result$error,
      output = out_safe$output,
      warnings = out_safe$warnings,
      messages = out_safe$messages)
  if(!is.null(out$error)){
    out$error <- conditionMessage(out$error)
  }
  out <- map(out, null_to_na)
  return(out)
}

null_to_na <- function(obj){
  if(is.null(obj)|(length(obj)==0)){
    return(NA)
  }else{
    return(obj)
  }
}

res <- map_dfr(a, ~safe_and_quiet(myf, .x))

which gives the desired output

# A tibble: 3 x 5
  result error    output warnings  messages
   <int> <chr>    <chr>  <chr>     <lgl>   
1      1 NA       ""     NA        NA      
2      2 NA       ""     a warning NA      
3     NA an error ""     NA        NA   

So I need a combination of safely and quietly as well as outputs that are not NULL or vectors of length 0 to be able to create a data frame.