AC-1989: Fix subset of deprecated php usages

- Fixes for php code

Author: Rrego6

app/code/Magento/Cron/Model/Config/Converter/Db.php

@@ -92,7 +92,7 @@ protected function _processScheduleParam(array $jobConfig, $jobName, array &$res
     protected function _processRunModel(array $jobConfig, $jobName, array &$result)
     {
         if (isset($jobConfig['run']) && is_array($jobConfig['run']) && array_key_exists('model', $jobConfig['run'])) {
-            $callPath = explode('::', $jobConfig['run']['model']);
+            $callPath = explode('::', $jobConfig['run']['model'] ?? '');
 
             if (empty($callPath) || empty($callPath[0]) || empty($callPath[1])) {
                 unset($result[$jobName]['run']);

app/code/Magento/CurrencySymbol/Block/Adminhtml/System/Currency/Rate/Matrix.php

@@ -107,7 +107,7 @@ protected function _prepareRates($array)
 
         foreach ($array as $key => $rate) {
             foreach ($rate as $code => $value) {
-                $parts = explode('.', $value);
+                $parts = explode('.', $value ?? '');
                 if (count($parts) == 2) {
                     $parts[1] = str_pad(rtrim($parts[1], 0), 4, '0', STR_PAD_RIGHT);
                     $array[$key][$code] = join('.', $parts);

app/code/Magento/Newsletter/Block/Adminhtml/Template/Edit.php

@@ -216,7 +216,7 @@ public function getForm()
      */
     public function getJsTemplateName()
     {
-        return addcslashes($this->getModel()->getTemplateCode(), "\"\r\n\\");
+        return addcslashes($this->getModel()->getTemplateCode() ?? '', "\"\r\n\\");
     }
 
     /**

app/code/Magento/SalesRule/Model/Quote/Discount.php

@@ -296,7 +296,7 @@ public function fetch(Quote $quote, Total $total)
             $description = $total->getDiscountDescription();
             $result = [
                 'code' => $this->getCode(),
-                'title' => strlen($description) ? __('Discount (%1)', $description) : __('Discount'),
+                'title' => strlen( is_string($description) ? $description : '') ? __('Discount (%1)', $description) : __('Discount'),
                 'value' => $amount
             ];
         }