DealValidator::checkFieldPresence

public function checkFieldPresence($fieldName, array &$messages = null)
{
	$message = null;
	if ($fieldName === 'TITLE')
	{
		$result = !$this->isNeedToCheck($fieldName)
			|| (is_string($this->entityFields[$fieldName])
				&& $this->entityFields[$fieldName] !== ''
				&& $this->entityFields[$fieldName] !== \CCrmDeal::GetDefaultTitle());
	}
	elseif($fieldName === 'OPPORTUNITY_WITH_CURRENCY')
	{
		$result = !$this->isNeedToCheck('OPPORTUNITY')
			||  (isset($this->entityFields['OPPORTUNITY']) && $this->entityFields['OPPORTUNITY'] > 0);

		if(!$result)
		{
			$message = Loc::getMessage(
				'CRM_ENTITY_VALIDATOR_FIELD_MUST_BE_GREATER_THEN_ZERO',
				array('%FIELD_NAME%' => \CCrmDeal::GetFieldCaption('OPPORTUNITY'))
			);
		}
	}
	elseif($fieldName === 'CLIENT')
	{
		$result = $this->clientValidator->checkPresence();
	}
	else if (Tracking\UI\Details::isTrackingField($fieldName))
	{
		$isNeedToCheck = $this->isNeedToCheck($fieldName);
		$isFilled = Tracking\UI\Details::isTrackingFieldFilled($this->entityFields);
		$result = !$isNeedToCheck || $isFilled;
		unset($isNeedToCheck, $isFilled);
	}
	else
	{
		if($fieldName === 'OBSERVER')
		{
			$effectiveFieldName = 'OBSERVER_IDS';
		}
		else
		{
			$effectiveFieldName = $fieldName;
		}
		$result = $this->innerCheckFieldPresence($effectiveFieldName);
	}

	if(!$result)
	{
		if($message === null)
		{
			$message = Loc::getMessage(
				'CRM_ENTITY_VALIDATOR_FIELD_IS_MISSING',
				array('%FIELD_NAME%' => \CCrmDeal::GetFieldCaption($fieldName))
			);
		}

		if(!is_array($messages))
		{
			$messages = array();
		}
		$messages[] = array('id' => $fieldName, 'text' => $message);
	}
	return $result;
}