CloudinaryImage underscore methods "not a function"

Expected behavior

When running an underscore function like "thumbnail" on a CloudinaryImage type with picture._.thumbnail(300,300) or perhaps even picture.thumbnail(300,300) it should output a cloudinary url with the appropriate transform. but this only works on the CloudinaryImages (Plural) type.

Actual/Current behavior

Throws errors, for example. If i set my "artist" model to have:

picture: { type: Types.CloudinaryImage, initial: true },

and in my view, attempt to use one of the underscore methods for example thumbnail:

img(src=artist.picture._.thumbnail(300,300))

I get:

Cannot read property 'thumbnail' of undefined

and when i try without the underscore:

img(src=artist.picture.thumbnail(300,300))

I get:

artist.picture.thumbnail is not a function

But if i change the type from CloudinaryImage to CloudinaryImages:

picture: { type: Types.CloudinaryImages, initial: true },

Then loop through:

if artist.picture each picture in artist.picture img(src=picture.thumbnail(300,300))

Then I get my desired result and i don't even need to use the ._. If i use the underscore I get this again.

Cannot read property 'thumbnail' of undefined

Steps to reproduce the actual/current behavior

See above

Environment

Software	Version
Keystone	4.0.0-beta.5
Node	8.2.1