The "standard" failure description is (e.g.):
{
"outcome" : "failed",
"failure-description" : [{
"PROPERTY_VALUE" :

{ "java.lang.IllegalArgumentException" : "Invalid key specification" }

}]
}

note "failure-description"

Sometimes it is different:

[localhost:9999 /] /server-group=new:add(profile=default)
{
"outcome" => "failed",
"result" =>

{"domain-failure-description" => [("java.lang.IllegalStateException" => "Resource at address [(\"server-group\" => \"new\")] already exists")]}

}

note "domain-failure-description".

Please unify that.