ArgumentNullException: Value cannot be null [FBX Exporter]

I've tried exporting a prefab as a Binary FBX and even tried as an ASCII FBX but I kepe getting this error.
I've tried on multiple versions of Unity, new packages and all, and to no avail. This error prevents the prefab from being exported. Help me, please!

 

I had the same problem. I had to manually check each child element of the prefab I want to export. I found there are Mesh Filters with NULL values assigned. I manually removed Mesh Filter components from the Inspector panel and re-exported the prefab to fbx. It worked.