diff --git a/.rector.php b/.rector.php
index b013daa88b..f03642946f 100644
--- a/.rector.php
+++ b/.rector.php
@@ -35,6 +35,7 @@
         DeadCode\ClassMethod\RemoveUselessReturnTagRector::class,
         DeadCode\MethodCall\RemoveNullArgOnNullDefaultParamRector::class,
         DeadCode\Property\RemoveUselessVarTagRector::class,
+        EarlyReturn\If_\ChangeNestedIfsToEarlyReturnRector::class,
         EarlyReturn\If_\RemoveAlwaysElseRector::class,
         Rector\CodingStyle\Rector\FuncCall\ConsistentImplodeRector::class,
         Rector\Php71\Rector\List_\ListToArrayDestructRector::class,
diff --git a/app/code/core/Mage/Adminhtml/Block/Catalog/Form/Renderer/Fieldset/Element.php b/app/code/core/Mage/Adminhtml/Block/Catalog/Form/Renderer/Fieldset/Element.php
index 1800a3bb08..9997ead5e6 100644
--- a/app/code/core/Mage/Adminhtml/Block/Catalog/Form/Renderer/Fieldset/Element.php
+++ b/app/code/core/Mage/Adminhtml/Block/Catalog/Form/Renderer/Fieldset/Element.php
@@ -58,15 +58,18 @@ public function getAttributeCode()
      */
     public function canDisplayUseDefault()
     {
-        if ($attribute = $this->getAttribute()) {
-            if (!$attribute->isScopeGlobal()
-                && $this->getDataObject()
-                && $this->getDataObject()->getId()
-                && $this->getDataObject()->getStoreId()
-            ) {
-                return true;
-            }
+        if (!$attribute = $this->getAttribute()) {
+            return false;
+        }
+
+        if (!$attribute->isScopeGlobal()
+            && $this->getDataObject()
+            && $this->getDataObject()->getId()
+            && $this->getDataObject()->getStoreId()
+        ) {
+            return true;
         }
+
         return false;
     }
 
diff --git a/app/code/core/Mage/Adminhtml/Block/Catalog/Product/Edit/Tab/Inventory.php b/app/code/core/Mage/Adminhtml/Block/Catalog/Product/Edit/Tab/Inventory.php
index 6b9ceadfbd..bde3f5af37 100644
--- a/app/code/core/Mage/Adminhtml/Block/Catalog/Product/Edit/Tab/Inventory.php
+++ b/app/code/core/Mage/Adminhtml/Block/Catalog/Product/Edit/Tab/Inventory.php
@@ -81,10 +81,12 @@ public function getFieldValueAsFloat(string $field): float
 
     public function getConfigFieldValue($field)
     {
-        if ($this->getStockItem()) {
-            if ($this->getStockItem()->getData('use_config_' . $field) == 0) {
-                return $this->getStockItem()->getData($field);
-            }
+        if (!$this->getStockItem()) {
+            return Mage::getStoreConfig(Mage_CatalogInventory_Model_Stock_Item::XML_PATH_ITEM . $field);
+        }
+
+        if ($this->getStockItem()->getData('use_config_' . $field) == 0) {
+            return $this->getStockItem()->getData($field);
         }
 
         return Mage::getStoreConfig(Mage_CatalogInventory_Model_Stock_Item::XML_PATH_ITEM . $field);
diff --git a/app/code/core/Mage/Bundle/Model/Sales/Order/Pdf/Items/Abstract.php b/app/code/core/Mage/Bundle/Model/Sales/Order/Pdf/Items/Abstract.php
index 66ab8b1766..fbb525cb25 100644
--- a/app/code/core/Mage/Bundle/Model/Sales/Order/Pdf/Items/Abstract.php
+++ b/app/code/core/Mage/Bundle/Model/Sales/Order/Pdf/Items/Abstract.php
@@ -147,12 +147,11 @@ public function isChildCalculated($item = null): bool
     public function getBundleOptions($item = null): array
     {
         $options = $this->getOrderItem()->getProductOptions();
-        if ($options) {
-            if (isset($options['bundle_options'])) {
-                return $options['bundle_options'];
-            }
+        if (!$options) {
+            return $options['bundle_options'] ?? [];
         }
-        return [];
+
+        return $options['bundle_options'] ?? [];
     }
 
     /**
diff --git a/app/code/core/Mage/Catalog/Block/Product/Abstract.php b/app/code/core/Mage/Catalog/Block/Product/Abstract.php
index 6e470662f2..ff55b09b9d 100644
--- a/app/code/core/Mage/Catalog/Block/Product/Abstract.php
+++ b/app/code/core/Mage/Catalog/Block/Product/Abstract.php
@@ -193,11 +193,14 @@ protected function _getPriceBlock($productTypeId)
      */
     protected function _getPriceBlockTemplate($productTypeId)
     {
-        if (isset($this->_priceBlockTypes[$productTypeId])) {
-            if ($this->_priceBlockTypes[$productTypeId]['template'] != '') {
-                return $this->_priceBlockTypes[$productTypeId]['template'];
-            }
+        if (!isset($this->_priceBlockTypes[$productTypeId])) {
+            return $this->_priceBlockDefaultTemplate;
+        }
+
+        if ($this->_priceBlockTypes[$productTypeId]['template'] != '') {
+            return $this->_priceBlockTypes[$productTypeId]['template'];
         }
+
         return $this->_priceBlockDefaultTemplate;
     }
 
diff --git a/app/code/core/Mage/Catalog/Model/Product/Type/Configurable.php b/app/code/core/Mage/Catalog/Model/Product/Type/Configurable.php
index 2b930e350e..92ce71ef00 100644
--- a/app/code/core/Mage/Catalog/Model/Product/Type/Configurable.php
+++ b/app/code/core/Mage/Catalog/Model/Product/Type/Configurable.php
@@ -727,11 +727,14 @@ public function getOrderOptions($product = null)
     #[\Override]
     public function isVirtual($product = null)
     {
-        if ($productOption = $this->getProduct($product)->getCustomOption('simple_product')) {
-            if ($optionProduct = $productOption->getProduct()) {
-                return $optionProduct->isVirtual();
-            }
+        if (!$productOption = $this->getProduct($product)->getCustomOption('simple_product')) {
+            return parent::isVirtual($product);
+        }
+
+        if ($optionProduct = $productOption->getProduct()) {
+            return $optionProduct->isVirtual();
         }
+
         return parent::isVirtual($product);
     }
 
diff --git a/app/code/core/Mage/Catalog/Model/Resource/Eav/Attribute.php b/app/code/core/Mage/Catalog/Model/Resource/Eav/Attribute.php
index ac37867922..912b19b6c2 100644
--- a/app/code/core/Mage/Catalog/Model/Resource/Eav/Attribute.php
+++ b/app/code/core/Mage/Catalog/Model/Resource/Eav/Attribute.php
@@ -243,11 +243,14 @@ public function getApplyTo()
     public function getSourceModel()
     {
         $model = $this->getData('source_model');
-        if (empty($model)) {
-            if ($this->getBackendType() == 'int' && $this->getFrontendInput() == 'select') {
-                return $this->getDefaultSourceModel();
-            }
+        if (!empty($model)) {
+            return $model;
+        }
+
+        if ($this->getBackendType() == 'int' && $this->getFrontendInput() == 'select') {
+            return $this->getDefaultSourceModel();
         }
+
         return $model;
     }
 
diff --git a/app/code/core/Mage/Core/Controller/Varien/Action.php b/app/code/core/Mage/Core/Controller/Varien/Action.php
index f0966de593..4ee3131053 100644
--- a/app/code/core/Mage/Core/Controller/Varien/Action.php
+++ b/app/code/core/Mage/Core/Controller/Varien/Action.php
@@ -797,16 +797,17 @@ protected function _getRefererUrl()
      */
     protected function _isUrlInternal($url)
     {
-        if (str_contains($url, 'http')) {
-            /**
-             * Url must start from base secure or base unsecure url
-             */
-            if (str_starts_with($url, Mage::app()->getStore()->getBaseUrl())
-                || str_starts_with($url, Mage::app()->getStore()->getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK, true))
-            ) {
-                return true;
-            }
+        if (!str_contains($url, 'http')) {
+            return false;
+        }
+
+        // Url must start from base secure or base unsecure url
+        if (str_starts_with($url, Mage::app()->getStore()->getBaseUrl())
+            || str_starts_with($url, Mage::app()->getStore()->getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK, true))
+        ) {
+            return true;
         }
+
         return false;
     }
 
diff --git a/app/code/core/Mage/Core/Helper/String.php b/app/code/core/Mage/Core/Helper/String.php
index 6f2d903b4a..0eec0c5b39 100644
--- a/app/code/core/Mage/Core/Helper/String.php
+++ b/app/code/core/Mage/Core/Helper/String.php
@@ -563,10 +563,12 @@ public function isSerializedArrayOrObject($data)
      */
     public function validateSerializedObject($str)
     {
-        if ($this->isSerializedArrayOrObject($str)) {
-            if (!unserialize($str)) {
-                return false;
-            }
+        if (!$this->isSerializedArrayOrObject($str)) {
+            return true;
+        }
+
+        if (!unserialize($str)) {
+            return false;
         }
 
         return true;
diff --git a/app/code/core/Mage/Customer/Model/Customer/Attribute/Backend/Password.php b/app/code/core/Mage/Customer/Model/Customer/Attribute/Backend/Password.php
index 643cb5a998..bb0aa91b81 100644
--- a/app/code/core/Mage/Customer/Model/Customer/Attribute/Backend/Password.php
+++ b/app/code/core/Mage/Customer/Model/Customer/Attribute/Backend/Password.php
@@ -49,10 +49,12 @@ public function beforeSave($object)
     #[\Override]
     public function validate($object)
     {
-        if ($password = $object->getPassword()) {
-            if ($password == $object->getPasswordConfirm()) {
-                return true;
-            }
+        if (!$password = $object->getPassword()) {
+            return parent::validate($object);
+        }
+
+        if ($password == $object->getPasswordConfirm()) {
+            return true;
         }
 
         return parent::validate($object);
diff --git a/app/code/core/Mage/Index/Model/Indexer/Abstract.php b/app/code/core/Mage/Index/Model/Indexer/Abstract.php
index 53c7f6a87c..c9eceec4cf 100644
--- a/app/code/core/Mage/Index/Model/Indexer/Abstract.php
+++ b/app/code/core/Mage/Index/Model/Indexer/Abstract.php
@@ -104,11 +104,14 @@ public function matchEvent(Mage_Index_Model_Event $event)
      */
     public function matchEntityAndType($entity, $type)
     {
-        if (isset($this->_matchedEntities[$entity])) {
-            if (in_array($type, $this->_matchedEntities[$entity])) {
-                return true;
-            }
+        if (!isset($this->_matchedEntities[$entity])) {
+            return false;
+        }
+
+        if (in_array($type, $this->_matchedEntities[$entity])) {
+            return true;
         }
+
         return false;
     }
 
diff --git a/app/code/core/Mage/Rss/Block/Catalog/Abstract.php b/app/code/core/Mage/Rss/Block/Catalog/Abstract.php
index 01d88cb6eb..01dc677252 100644
--- a/app/code/core/Mage/Rss/Block/Catalog/Abstract.php
+++ b/app/code/core/Mage/Rss/Block/Catalog/Abstract.php
@@ -71,11 +71,14 @@ protected function _getPriceBlock($productTypeId)
      */
     protected function _getPriceBlockTemplate($productTypeId)
     {
-        if (isset($this->_priceBlockTypes[$productTypeId])) {
-            if ($this->_priceBlockTypes[$productTypeId]['template'] != '') {
-                return $this->_priceBlockTypes[$productTypeId]['template'];
-            }
+        if (!isset($this->_priceBlockTypes[$productTypeId])) {
+            return $this->_priceBlockDefaultTemplate;
+        }
+
+        if ($this->_priceBlockTypes[$productTypeId]['template'] != '') {
+            return $this->_priceBlockTypes[$productTypeId]['template'];
         }
+
         return $this->_priceBlockDefaultTemplate;
     }