fix warn

lib/potent-reducer.js

@@ -91,6 +91,7 @@ export const createStore = options => {
 }
 
 function assertSelectedExists(value) {
+  if (typeof value !== 'undefined') return
   console.warn(`A selector returned undefined.
 This indicates that you tried to access a state property that does not exist.
 To turn these messages off use {"warnOnUndefinedSelect": false} in options`)