Creating an asset example fails on process_file

[gilest]

Following along from README.md.

    image_file = Contentful::Management::File.new
    image_file.properties[:contentType] = 'image/jpeg'
    image_file.properties[:fileName] = "#{@artist.slug}.jpg"
    image_file.properties[:upload] = @artist.image

    asset = @environment.assets.create(title: @artist.slug, description: '', file: image_file)
    asset.save

    asset.process_file

Fails with this error:

Message: Validation error
Details:
	* Name: required - Path: '["fields", "file", "en-US", "upload"]' - Value: ''
	* Name: required - Path: '["fields", "file", "en-US", "uploadFrom"]' - Value: ''
Request ID: xyz
/Users/giles/.gem/ruby/2.3.1/gems/contentful-management-2.11.0/lib/contentful/management/client.rb:390:in `execute_request'

It seems that some properties are missing on the asset.file object.

The following snippet completes without error:

    image_file = Contentful::Management::File.new
    image_file.properties[:contentType] = 'image/jpeg'
    image_file.properties[:fileName] = "#{@artist.slug}.jpg"
    image_file.properties[:upload] = @artist.image

    asset = @environment.assets.create(title: @artist.slug, description: '', file: image_file)

    asset.file.properties[:contentType] = 'image/jpeg'
    asset.file.properties[:fileName] = "#{@artist.slug}.jpg"
    asset.file.properties[:upload] = @artist.image

    asset.save

    asset.process_file