public final void assignOwner(DataList<DATATYPE> owner) {
        if (this.owner != null) throw new NullPointerException("Owner of " + this + " was already assigned");
        this.owner = owner;
    }
Assigns the owner of this. Throws an exception if the owner is already set.
container-core/src/main/java/com/yahoo/processing/response/DefaultIncomingData.java