I have Magento 1.9.3.10 with the patch for PHP 7.2 applied. If I click "add to cart" on a product that has options and no options are selected, I get this error:
Exception: Warning: count(): Parameter must be an array or an object that implements Countable in /var/www/html/app/code/core/Mage/Catalog/Model/Product/Option/Type/Select.php on line 57 in /var/www/html/app/code/core/Mage/Core/functions.php:232 Stack trace: #0 /var/www/html/app/code/core/Mage/Catalog/Model/Product/Option/Type/Select.php(57): mageCoreErrorHandler(2, 'count(): Parame...', '/var/www/html/a...', 57, Array) #1 /var/www/html/app/code/core/Mage/Catalog/Model/Product/Type/Abstract.php(533): Mage_Catalog_Model_Product_Option_Type_Select->validateUserValue(NULL) #2 /var/www/html/app/code/core/Mage/Catalog/Model/Product/Type/Abstract.php(322): Mage_Catalog_Model_Product_Type_Abstract->_prepareOptions(Object(Varien_Object), Object(Mage_Catalog_Model_Product), 'full') #3 /var/www/html/app/code/core/Mage/Catalog/Model/Product/Type/Abstract.php(410): Mage_Catalog_Model_Product_Type_Abstract->_prepareProduct(Object(Varien_Object), Object(Mage_Catalog_Model_Product), 'full') #4 /var/www/html/app/code/core/Mage/Sales/Model/Quote.php(969): Mage_Catalog_Model_Product_Type_Abstract->prepareForCartAdvanced(Object(Varien_Object), Object(Mage_Catalog_Model_Product), 'full') #5 /var/www/html/app/code/core/Mage/Sales/Model/Quote.php(1045): Mage_Sales_Model_Quote->addProductAdvanced(Object(Mage_Catalog_Model_Product), Object(Varien_Object), 'full') #6 /var/www/html/app/code/core/Mage/Checkout/Model/Cart.php(268): Mage_Sales_Model_Quote->addProduct(Object(Mage_Catalog_Model_Product), Object(Varien_Object)) #7 /var/www/html/app/code/core/Mage/Checkout/controllers/CartController.php(235): Mage_Checkout_Model_Cart->addProduct(Object(Mage_Catalog_Model_Product), Array) #8 /var/www/html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Checkout_CartController->addAction() #9 /var/www/html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('add') #10 /var/www/html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http)) #11 /var/www/html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch() #12 /var/www/html/app/Mage.php(686): Mage_Core_Model_App->run(Array) #13 /var/www/html/index.php(85): Mage::run('', 'store') #14 {main}