static public function isNull(QtiDatatype $value = null)
    {
        return is_null($value) === true || ($value instanceof QtiString && $value->getValue() === '') || ($value instanceof Container && count($value) === 0);
    }
static public function isNull(QtiDatatype $value = null)
    {
        return is_null($value) === true || ($value instanceof QtiString && $value->getValue() === '') || ($value instanceof Container && count($value) === 0);
    }
static public function isNull ( QtiDatatype $ value = null ) { return is_null ( $ value ) === true || ( $ value instanceof QtiString && $ value -> getValue ( ) === '' ) || ( $ value instanceof Container && count ( $ value ) === 0 ) ; }
Whether or not a QtiDatatype is considered to be null.

As per the QTI specification, the NULL value, empty strings and empty containers
are always treated as NULL values.

@param \qtism\common\datatypes\QtiDatatype $value
@return boolean
Whether or not a QtiDatatype is considered to be null .