Xa-datasource:add requires a non-empty map "xa-data-source-properties", which is not documented

[domain@localhost:9999 subsystem=datasources] ./xa-data-source=xa-ds:read-operation-description(name=add)
does not list a (required) property "xa-data-source-properties", but when this is not provided, adding a xa-datasource fails and console shows

[Server:server-two] 15:25:52,983 WARN [org.jboss.as.controller] (pool-1-thread-35) Operation ("add") failed - address: ([
[Server:server-two] ("subsystem" => "datasources"),
[Server:server-two] ("xa-data-source" => "postgres")
[Server:server-two] ]): java.lang.IllegalArgumentException

Adding an empty xa-data-source-properties map also makes the :add fail. It only works when this property is present and some (dummy!) values are given.

1) the requirement for this xa-da.. should be documented
2) it should be optional
3) an empty map should be allowed (if no xa-props are needed)