hollow/src/main/java/com/netflix/hollow/core/index/HollowPrefixIndex.java
public boolean contains(String key) {
        if (key == null) throw new IllegalArgumentException("key cannot be null");
        TST current;
        boolean result;
        do {
            current = prefixIndexVolatile;
            result = current.contains(key);
        } while (current != this.prefixIndexVolatile);
        return result;
    }
public boolean contains(String key) {
        if (key == null) throw new IllegalArgumentException("key cannot be null");
        TST current;
        boolean result;
        do {
            current = prefixIndexVolatile;
            result = current.contains(key);
        } while (current != this.prefixIndexVolatile);
        return result;
    }
Check if the given key exists in the index.

@param key the key
@return {@code true} if the key exists, otherwise {@code false}