In normal bash, when no results found while using reverse-i-search (Ctrl+R), you still able to run the command you started to type.

In fish, if search fails, pressing enter just cancels the search.

I think fish should stick to bash behavior in here, – actually execute command on pressing Enter.

After all, if user wants to cancel his command, he can always press Ctrl+C.

There's no need to duplicate this behavior for Enter, basically removing other useful functionality.