ninja-core/src/main/java/ninja/cache/NinjaCache.java
public void add(String key, Object value, String expiration) {
        checkSerializable(value);
        cache.add(key, value, TimeUtil.parseDuration(expiration));
    }
public void add(String key, Object value, String expiration) {
        checkSerializable(value);
        cache.add(key, value, TimeUtil.parseDuration(expiration));
    }
Add an element only if it doesn't exist.
@param key Element key
@param value Element value
@param expiration Ex: 10s, 3mn, 8h