PHP8: base64_decode(): Passing null is deprecated (OpenMage#4281)

* PHP8: base64_decode(): Passing null to parameter #1 ($string) of type string is deprecated

- OpenMage#4243 (comment)

* refactor

* refactor

* refactor

* refactor [skip ci]

* Update app/code/core/Mage/Adminhtml/Block/Sales/Order/Grid.php

Co-authored-by: Ng Kiat Siong <[email protected]>

---------

Co-authored-by: Ng Kiat Siong <[email protected]>

Author: sreichel

app/code/core/Mage/Adminhtml/Block/Sales/Order/Grid.php

@@ -141,21 +141,38 @@ protected function _prepareColumns()
             );
         }
 
+        $this->addRssFeedLink();
+
+        $this->addExportType('*/*/exportCsv', Mage::helper('sales')->__('CSV'));
+        $this->addExportType('*/*/exportExcel', Mage::helper('sales')->__('Excel XML'));
+
+        return parent::_prepareColumns();
+    }
+
+    /**
+     * Add link to RSS feed when enabled for filtered store-view
+     *
+     * @return $this
+     * @throws Mage_Core_Model_Store_Exception
+     */
+    public function addRssFeedLink()
+    {
         if (Mage::helper('sales')->isModuleOutputEnabled('Mage_Rss')) {
-            $filterString = $this->getParam($this->getVarNameFilter());
-            $filter = Mage::helper('adminhtml')->prepareFilterString($filterString);
-            $storeId = array_key_exists('store_id', $filter) ? $filter['store_id'] : null;
+            $storeId = null;
+
+            $filterString = $this->getParam($this->getVarNameFilter(), '');
+            if ($filterString) {
+                $filter = Mage::helper('adminhtml')->prepareFilterString($filterString);
+                $storeId = $filter['store_id'] ?? null;
+            }
 
             if (Mage::helper('rss')->isRssAdminOrderNewEnabled($storeId)) {
                 $slug = $storeId ? '/store/' . $storeId : '';
                 $this->addRssList('rss/order/new' . $slug, Mage::helper('sales')->__('New Order RSS'));
             }
         }
 
-        $this->addExportType('*/*/exportCsv', Mage::helper('sales')->__('CSV'));
-        $this->addExportType('*/*/exportExcel', Mage::helper('sales')->__('Excel XML'));
-
-        return parent::_prepareColumns();
+        return $this;
     }
 
     /**

app/code/core/Mage/Adminhtml/Block/Widget/Grid.php

@@ -372,7 +372,7 @@ public function removeColumn($columnId)
      * @param string $columnId
      * @param array|Varien_Object $column
      * @param string $after
-     * @return  Mage_Adminhtml_Block_Widget_Grid
+     * @return $this
      * @throws Exception
      */
     public function addColumnAfter($columnId, $column, $after)
@@ -964,7 +964,7 @@ public function getExportTypes()
      *
      * @param   string $url
      * @param   string $label
-     * @return  Mage_Adminhtml_Block_Widget_Grid
+     * @return  $this
      */
     public function addExportType($url, $label)
     {
@@ -1010,7 +1010,7 @@ protected function _getRssUrl($url)
      *
      * @param string $url
      * @param string $label
-     * @return  Mage_Adminhtml_Block_Widget_Grid
+     * @return  $this
      * @throws Mage_Core_Model_Store_Exception
      */
     public function addRssList($url, $label)
@@ -1757,7 +1757,7 @@ public function getRowspan($item, $column)
     /**
      * @param string|object $column
      * @param string $value
-     * @return bool|Mage_Adminhtml_Block_Widget_Grid
+     * @return bool|$this
      */
     public function isColumnGrouped($column, $value = null)
     {