Cache NPE issue

[FqqCS]

In Class：io.fabric8.kubernetes.client.informers.cache.Cache

In method "replace" , if arg "list" is empty; this.indices will be set to an empty hashmap. in method "byIndex",object "index" used without check NPE, so when watch a kind without any resource, and then using byIndex to get, NPE happened. maybe should return an empty object instead of throw NPE.

// In byIndex
Map<String, Set> index = this.indices.get(indexName);
Set set = index.get(indexKey);

public synchronized void replace(List list, String resourceVersion) {
Map<String, T> newItems = new HashMap<>();
for (T item : list) {
String key = keyFunc.apply(item);
newItems.put(key, item);
}
this.items = newItems;

// rebuild any index
**this.indices = new HashMap<>();**
for (Map.Entry<String, T> itemEntry : items.entrySet()) {
  this.updateIndices(null, itemEntry.getValue(), itemEntry.getKey());
}

}