There is a case that fileReference is set as an array in the JCR.
This happens when there is an image, which already has an asset set, editing it, clearing the reference and setting a new image.
Setup a new AEM 6.5 author on port 4502
Create a sample project using wcm.io archetype
Using example from "AEM project with wcm.io and Sling-Initial-Content project layout and Java 11"
Install the sample project “./build-deploy.sh”
Add an image component, set an image, save
Edit that component, press “Clear”, save
Edit that component, set an image, save
I tried the Adobe core component:
set sling:resourceSuperType to core/wcm/components/image/v2/image
The problem does not occur