Getting image url of CMSEditableImage in webpart code

I need to get the url of the image in code-behind because I need to use as a background image. .ImageControl is always null.There is some code here (https://devnet.kentico.com/questions/retrieve-image-url-from-cms-cmseditableimage-in-code) but this relates to to an ASPX page, not a web-part and it doesn't work.