def fetch_value(key)
      val = fetch_nested(key)
      return val if self[:no_pruning].include?(key)
      Prunable::VALUES.include?(val) ? Prunable::Value : val
    end
def fetch_value(key)
      val = fetch_nested(key)
      return val if self[:no_pruning].include?(key)
      Prunable::VALUES.include?(val) ? Prunable::Value : val
    end
returns Prunable::Value if the value is in VALUES (called from stringified)