public static String hide(final String key) {
            return isHidden(key) ? key : HIDDEN_PREFIX.concat(key);
        }
Turn the provided key into a hidden key. If the key is already a hidden key, return key.

@param key The key to make a hidden key
@return The hidden key
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/Graph.java