mappedby field of embedded document throws notice

Currently working on a versioned tree structure where the parent of the Category is referenced from the embedded CategoryVersion.

This works perfectly, but the only problem is that it throws a notice in de DocumentPersister at line 708.

Example of the structure:

    Class Category
    {
        /** @ODM\Id(strategy="AUTO") */
        private $id;
    
        /** @ODM\EmbedOne(targetDocument="CategoryVersion") */
        private $version;
    
        /** @ODM\EmbedMany(targetDocument="CategoryVersion") */
        private $versions;
    
        /**
         * @ODM\ReferenceMany(
         *      targetDocument="Category",
         *      cascade={"all"},
         *      mappedBy="version.parent",
         *      sort={"version.sequence"="asc"}
         * )
         */
        private $children;
    }
    
    /** @ODM\EmbeddedDocument */
    class CategoryVersion
    {
        /** @ODM\Field(type="int") */
        private $sequence = 0;
    
        /** @ODM\ReferenceOne(targetDocument="Category", cascade={"all"}, inversedBy="children") */
        private $parent;
    }