Hi Matt,
Thank you for confirming this issue. Yes, I was able to work around it with Arcade expression. When the image url is empty, I just use a placeholder image instead. The bubble will look like below. It looks better than the empty image but not as good as fully hide the image area.
Here is the Arcade expression:
{
"popupInfo": {
"title": "{Name}",
"fieldInfos": [...],
"expressionInfos": [{
"name": "expr0",
"title": "ImageUrl",
"expression": "IIf(IsEmpty($feature.Thumbnail),'http://hazegazer.org/assets/image/img_not_available.png',$feature.Thumbnail)",
"returnType": "string"
}],
"mediaInfos": [{
"title": "Image",
"type": "image",
"value": {
"sourceURL": "{expression/expr0}",
"linkURL": "{Image}"
}
}]
}
}