[base] Fix ambient type issue

packages/@sanity/base/src/user-color/hooks.ts

@@ -1,5 +1,5 @@
 import {useContext} from 'react'
-import {of} from 'rxjs'
+import {empty} from 'rxjs'
 import {useObservable} from '../util/useObservable'
 import {UserColorManagerContext} from './context'
 import {UserColor, UserColorManager} from './types'
@@ -11,5 +11,5 @@ export function useUserColorManager(): UserColorManager {
 export function useUserColor(userId: string | null): UserColor {
   const manager = useUserColorManager()
 
-  return useObservable(userId === null ? of(manager.get(null)) : manager.listen(userId))
+  return useObservable(userId ? manager.listen(userId) : empty(), manager.get(null))
 }