Illegal Argument error while using REST API for crucible

I am trying to create a post request object to attach a file to my review using the REST API to addFile. While recreating the request object in postman:

  1. I have set the content-type to multipart/form-data and assigned a boundary to it as well.
  2. I have in the body added the file to be uploaded.

The result of the request when sent returns an Illegal Argument Error as shown below:

    <message>fileToReview cannot be be null</message>

I have recreated the post request as intercepted by the browser which runs an html form that calls on to the same API. In that scenario it works fine, but running it with postman doesn’t seem to do so.
Is there an error in my method of recreating the request object?
How should I actually utilise the REST API?

Dev Environment:
Language -> Java
Framework -> Eclipse RCP