@Nullable open fun requestBodyConverter(type: Type!, parameterAnnotations: Array<Annotation!>!, methodAnnotations: Array<Annotation!>!, retrofit: Retrofit!): Converter<*, RequestBody!>?
Returns a Converter for converting type to an HTTP request body, or null if type cannot be handled by this factory. This is used to create converters for types specified by @Body, @Part, and @PartMap values.