Say a Wizard casts Find Familiar for himself, and then casts it again into a Ring of Spell Storing. The Ring is then given to another person, let's say a Rogue, who uses the Ring to cast Find Familiar.
The description of Find Familiar says
If you cast this spell while you already have a familiar, you instead cause it to adopt a new form.
but the description of the Ring says
The spell has no effect, other than to be stored in the ring.
What happens? Does the Wizard's familiar change when the spell is cast into the Ring? Does it change when the spell is cast out of the Ring? Does the Rogue get a Familiar, since the Rogue is considered to be casting the spell?