PLINK2-10 added support for AttributeValue elements with nested elements. However, this 'fix' introduced another issue. Namely, when an AttributeValue exists but its empty it.

Any of these occurences fail:

<saml2:AttributeValue />

<saml2:AttributeValue><saml2:AttributeValue/>

throwing a "java.lang.RuntimeException: PL00069: Parser: Type not supported:AttributeValue"

A 'workaround' is to add the 'type', e.g.

<saml2:AttributeValue xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string" />

However, the spec states that:

The <AttributeValue> element supplies the value of a specified SAML attribute. It is of the xs:anyType type, which allows any well-formed XML to appear as the content of the element. If the data content of an <AttributeValue> element is of an XML Schema simple type (such as xs:integer or xs:string), the datatype MAY be declared explicitly by means of an xsi:type declaration in the <AttributeValue> element.

And with regard to the empty values:

If a SAML attribute includes an empty value, such as the empty string,
the corresponding
<AttributeValue> element MUST be empty (generally this is serialized
as <AttributeValue/>)