mapping runtime attribute of undertow returns different type than described in r-r-d

"mappings" => {
    "type" => LIST,
    "description" => "Servlet mappings",
    "expressions-allowed" => false,
    "required" => false,
    "nillable" => true,
    "min-length" => 0L,
    "max-length" => 2147483647L,
    "value-type" => STRING,
    "access-type" => "metric",
    "storage" => "runtime"
},

/host=master/server=server-one/deployment=helloworld.war/subsystem=undertow/servlet=*:read-resource(include-runtime)
{
    "outcome" => "success",
    "result" => [{
        "address" => [
            ("host" => "master"),
            ("server" => "server-one"),
            ("deployment" => "helloworld.war"),
            ("subsystem" => "undertow"),
            ("servlet" => "org.jboss.as.quickstarts.helloworld.HelloWorldServlet")
        ],
        "outcome" => "success",
        "result" => {
            "mappings" => 0,
            "max-request-time" => 0,
            "min-request-time" => 0,
            "request-count" => 0,
            "servlet-class" => "org.jboss.as.quickstarts.helloworld.HelloWorldServlet",
            "servlet-name" => "org.jboss.as.quickstarts.helloworld.HelloWorldServlet",
            "total-request-time" => 0
        }
    }]
}