Login with no service extensions serialize to invalid XML EPP document

[kmkaplan]

When the ext_uris argument to Login::new() is None, Login serializes to and XML document that is invalid against the EPP schema. That's because it outputs an empty <svcExtension/> element, whereas the schema is:

<complexType name="loginSvcType">
  <sequence>
    <element name="objURI" type="anyURI"
     maxOccurs="unbounded"/>
    <element name="svcExtension" type="epp:extURIType"
     minOccurs="0"/>
  </sequence>
</complexType>
<complexType name="extURIType">
  <sequence>
    <element name="extURI" type="anyURI"
     maxOccurs="unbounded"/>
  </sequence>
</complexType>

That means that the <svcExtension> element must contain at least one <extURI> element, it can not be empty. To indicate no service extension the <svcExtension> element should be omited.

Example of generated bogus XML:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
  <command>
    <login>
      <clID>username</clID>
      <pw>password</pw>
      <options>
        <version>1.0</version>
        <lang>en</lang>
      </options>
      <svcs>
        <objURI>urn:ietf:params:xml:ns:host-1.0</objURI>
        <objURI>urn:ietf:params:xml:ns:contact-1.0</objURI>
        <objURI>urn:ietf:params:xml:ns:domain-1.0</objURI>
        <svcExtension/>
      </svcs>
    </login>
    <clTRID>cltrid:1626454866</clTRID>
  </command>
</epp>