Returns an appropriate representation of the data contained within a request body based on its encoding.
pluck_body(x)
one of the following:
NULL
if the request is not associated with a body
NULL
if an upload is used not in a list
list containing the multipart-encoded body
character vector with the JSON- or raw-encoded body, or upload form file
an unexecuted crul, httr or httr2 request object