Example code in documentation section "7.1.5.1 Testing the existance of a relation" (listing .12) doesn't work.

$obj = new Model();
if(isset($obj->Relation())) { // returns false
        ...
}
$obj->Relation = new Relation();
if(isset($obj->Relation())) { // returns true
        ...
}

The "if" condition results in PHP fatal error "Can't use method return value in write context...".