def update_attribute(key, value)
      unless attribute?(key.to_sym)
        raise Error::UnknownAttribute.new(attribute: key)
      end

      _attributes[key.to_sym] = value
    end
def update_attribute(key, value)
      unless attribute?(key.to_sym)
        raise Error::UnknownAttribute.new(attribute: key)
      end

      _attributes[key.to_sym] = value
    end
Update a single attribute in the attributes hash.

 @raise