function validateNumber($value) {
		$minValue=$this->getNumberMinValue();
		$maxValue=$this->getNumberMaxValue();
		
		if ($value === null && $this->minLength > 0)
			return $this->errorTooShort.$this->minLength;
		
		if ($value === null) return null;
		
		return $this->validate_min_max($value, $minValue, $maxValue);
	}