/**
     * Returns the updated source map by merging with existing source.
     * @param existingSource The existing source map.
     * @return The updated source map.
     */
    public Map<String, Object> getUpdatedSource(final Map<String, Object> existingSource) {
        return SuggestItemSerializer.toUpdatedSource(this, existingSource);
    }

    /**
     * Concatenates values to a destination list, avoiding duplicates.