def get_if_handleable value
      case value
      when String then value
      when DateTime then value.to_time.utc.xmlschema(3)
      else nil
      end
    end
def get_if_handleable value
      case value
      when String then value
      when DateTime then value.to_time.utc.xmlschema(3)
      else nil
      end
    end
This method is used because, for nil values, savon will respond with an hash containing all other attributes.
 If we check that the expected type is matched, we can
 prevent to retrieve wrong values