AssetTagHelper::image_path outside views

Question

Supposedly, ActionController::Base.helpers acts like a proxy for accessing helpers outside views. However many of the methods defined there rely on controller variables and I'm unable to succesfully call:

ActionController::Base.helpers.image_path("my_image.png")
>> TypeError Exception: can't convert nil into String

Digging at the source I see compute_asset_host method is trying to access config.asset_host but config is nil.

How can I successfully call image_path from outside views?