diff --git a/app/code/Magento/Tax/Model/Calculation/Rate.php b/app/code/Magento/Tax/Model/Calculation/Rate.php
index f639d6680a7fc039b95e3617c63f3664b1134e1d..9e44cd113ddeaa7d4b0ff1704c70edcb12a76df6 100644
--- a/app/code/Magento/Tax/Model/Calculation/Rate.php
+++ b/app/code/Magento/Tax/Model/Calculation/Rate.php
@@ -227,7 +227,7 @@ class Rate extends \Magento\Framework\Model\AbstractExtensibleModel implements T
      */
     public function saveTitles($titles = null)
     {
-        if (is_null($titles)) {
+        if ($titles === null) {
             $titles = $this->getTitle();
         }
 
@@ -256,7 +256,7 @@ class Rate extends \Magento\Framework\Model\AbstractExtensibleModel implements T
      */
     public function getTitleModel()
     {
-        if (is_null($this->_titleModel)) {
+        if ($this->_titleModel === null) {
             $this->_titleModel = $this->_titleFactory->create();
         }
         return $this->_titleModel;
@@ -270,7 +270,7 @@ class Rate extends \Magento\Framework\Model\AbstractExtensibleModel implements T
         if ($this->getData(self::KEY_TITLES)) {
             return $this->getData(self::KEY_TITLES);
         }
-        if (is_null($this->_titles)) {
+        if ($this->_titles === null) {
             $this->_titles = $this->getTitleModel()->getCollection()->loadByRateId($this->getId())->getItems();
         }
         return $this->_titles;
diff --git a/app/code/Magento/Tax/Model/Sales/Total/Quote/CommonTaxCollector.php b/app/code/Magento/Tax/Model/Sales/Total/Quote/CommonTaxCollector.php
index 1fcaf0e413cd5e6f7ba077422f9a59e998956f27..7752911ceb22f59bb0523623cbe20a913d3041db 100644
--- a/app/code/Magento/Tax/Model/Sales/Total/Quote/CommonTaxCollector.php
+++ b/app/code/Magento/Tax/Model/Sales/Total/Quote/CommonTaxCollector.php
@@ -771,7 +771,7 @@ class CommonTaxCollector extends AbstractTotal
                 $previouslyAppliedTaxes[$row['id']] = $row;
             }
 
-            if (!is_null($row['percent'])) {
+            if ($row['percent'] !== null) {
                 $row['percent'] = $row['percent'] ? $row['percent'] : 1;
                 $rate = $rate ? $rate : 1;