appendFormFile
fun appendFormFile(controlName: String, filename: String? = null, contentType: String? = null, body: <Error class: unknown class>)
Adds a new MIME part containing @body to @multipart
Uses "Content-Disposition: form-data", as per the HTML forms specification.
Parameters
controlName
the name of the control associated with this file
filename
the name of the file, or null if not known
contentType
the MIME type of the file, or null if not known
body
the file data