public function applyDefaultValue()
    {
        parent::applyDefaultValue();

        if (is_null($this->getDefaultValue()) === true && $this->getCardinality() === Cardinality::SINGLE) {
            if ($this->getBaseType() === BaseType::INTEGER) {
                $this->setValue(new QtiInteger(0));
            } elseif ($this->getBaseType() === BaseType::FLOAT) {
                $this->setValue(new QtiFloat(0.0));
            }
        }
    }