def validate_required_attributes!
      unless required_attributes?
        blank_attribute = required_attributes.detect { |attr| self[attr].nil? || self[attr].empty? }

        raise ValidationError, "#{blank_attribute} can't be blank"
      end
    end
def validate_required_attributes!
      unless required_attributes?
        blank_attribute = required_attributes.detect { |attr| self[attr].nil? || self[attr].empty? }

        raise ValidationError, "#{blank_attribute} can't be blank"
      end
    end
Validate required attributes to be filled. Raises an exception
 if one of the attribute is not specified.

 @raise [AlphaCard::InvalidObjectError] error if required attributes not set