diff --git a/app/code/core/Mage/Catalog/Model/Resource/Category/Flat.php b/app/code/core/Mage/Catalog/Model/Resource/Category/Flat.php
index 8256201bd8d..13d86cddb17 100644
--- a/app/code/core/Mage/Catalog/Model/Resource/Category/Flat.php
+++ b/app/code/core/Mage/Catalog/Model/Resource/Category/Flat.php
@@ -31,56 +31,56 @@ class Mage_Catalog_Model_Resource_Category_Flat extends Mage_Index_Model_Resourc
      *
      * @var int|null
      */
-    protected $_storeId                  = null;
+    protected $_storeId = null;
 
     /**
      * Loaded
      *
      * @var bool
      */
-    protected $_loaded                   = false;
+    protected $_loaded = false;
 
     /**
      * Nodes
      *
      * @var array
      */
-    protected $_nodes                    = [];
+    protected $_nodes = [];
 
     /**
      * Columns
      *
      * @var array
      */
-    protected $_columns                  = null;
+    protected $_columns = null;
 
     /**
      * Columns sql
      *
      * @var array
      */
-    protected $_columnsSql               = null;
+    protected $_columnsSql = null;
 
     /**
      * Attribute codes
      *
      * @var array
      */
-    protected $_attributeCodes           = null;
+    protected $_attributeCodes = null;
 
     /**
      * Inactive categories ids
      *
      * @var array
      */
-    protected $_inactiveCategoryIds      = null;
+    protected $_inactiveCategoryIds = null;
 
     /**
      * Store flag which defines if Catalog Category Flat Data has been initialized
      *
      * @var array
      */
-    protected $_isBuilt                  = [];
+    protected $_isBuilt = [];
 
     /**
      * Store flag which defines if Catalog Category Flat Data has been initialized
@@ -89,7 +89,7 @@ class Mage_Catalog_Model_Resource_Category_Flat extends Mage_Index_Model_Resourc
      *
      * @var bool|null
      */
-    protected $_isRebuilt                = null;
+    protected $_isRebuilt = null;
 
     /**
      * array with root category id per store
@@ -103,7 +103,7 @@ class Mage_Catalog_Model_Resource_Category_Flat extends Mage_Index_Model_Resourc
      *
      * @var bool
      */
-    protected $_allowTableChanges        = true;
+    protected $_allowTableChanges = true;
 
     /**
      * Factory instance
@@ -658,7 +658,7 @@ protected function _getStaticColumns()
             }
             $_is_unsigned = '';
             $ddlType = $helper->getDdlTypeByColumnType($column['DATA_TYPE']);
-            $column['DEFAULT'] = trim($column['DEFAULT'], "' ");
+            $column['DEFAULT'] = empty($column['DEFAULT']) ? $column['DEFAULT'] : trim($column['DEFAULT'], "' ");
             switch ($ddlType) {
                 case Varien_Db_Ddl_Table::TYPE_SMALLINT:
                 case Varien_Db_Ddl_Table::TYPE_INTEGER:
diff --git a/app/code/core/Mage/Core/Helper/String.php b/app/code/core/Mage/Core/Helper/String.php
index 80804850d94..de0b038e6d7 100644
--- a/app/code/core/Mage/Core/Helper/String.php
+++ b/app/code/core/Mage/Core/Helper/String.php
@@ -44,7 +44,7 @@ class Mage_Core_Helper_String extends Mage_Core_Helper_Abstract
     public function truncate($string, $length = 80, $etc = '...', &$remainder = '', $breakWords = true)
     {
         $remainder = '';
-        if ($length == 0) {
+        if (is_null($string) || $length == 0) {
             return '';
         }
 
@@ -75,7 +75,7 @@ public function truncate($string, $length = 80, $etc = '...', &$remainder = '',
      */
     public function strlen($string)
     {
-        return iconv_strlen($string, self::ICONV_CHARSET);
+        return is_null($string) ? 0 : iconv_strlen($string, self::ICONV_CHARSET);
     }
 
     /**
@@ -88,6 +88,9 @@ public function strlen($string)
      */
     public function substr($string, $offset, $length = null)
     {
+        if (is_null($string)) {
+            return '';
+        }
         $string = $this->cleanString($string);
         if (is_null($length)) {
             $length = $this->strlen($string) - $offset;
@@ -246,6 +249,9 @@ public function str_split($str, $length = 1, $keepWords = false, $trim = false,
      */
     public function splitWords($str, $uniqueOnly = false, $maxWordLength = 0, $wordSeparatorRegexp = '\s')
     {
+        if (is_null($str)) {
+            return [];
+        }
         $result = [];
         $split = preg_split('#' . $wordSeparatorRegexp . '#siu', $str, -1, PREG_SPLIT_NO_EMPTY);
         foreach ($split as $word) {
@@ -269,8 +275,12 @@ public function splitWords($str, $uniqueOnly = false, $maxWordLength = 0, $wordS
      */
     public function cleanString($string)
     {
-        return '"libiconv"' == ICONV_IMPL ?
-            iconv(self::ICONV_CHARSET, self::ICONV_CHARSET . '//IGNORE', $string) : $string;
+        if (is_null($string)) {
+            return '';
+        }
+        return '"libiconv"' == ICONV_IMPL
+            ? iconv(self::ICONV_CHARSET, self::ICONV_CHARSET . '//IGNORE', $string)
+            : $string;
     }
 
     /**
@@ -279,11 +289,11 @@ public function cleanString($string)
      * @param string $haystack
      * @param string $needle
      * @param int $offset
-     * @return int
+     * @return int|false
      */
-    public function strpos($haystack, $needle, $offset = null)
+    public function strpos($haystack, $needle, $offset = 0)
     {
-        return iconv_strpos($haystack, $needle, $offset, self::ICONV_CHARSET);
+        return iconv_strpos((string) $haystack, (string) $needle, $offset, self::ICONV_CHARSET);
     }
 
     /**
@@ -315,6 +325,9 @@ public function ksortMultibyte(array &$sort)
      */
     public function parseQueryStr($str)
     {
+        if (is_null($str)) {
+            return [];
+        }
         $argSeparator = '&';
         $result = [];
         $partsQueryStr = explode($argSeparator, $str);
@@ -510,6 +523,9 @@ public function uniOrd($c)
      */
     public function unserialize($str)
     {
+        if (is_null($str)) {
+            return null;
+        }
         $reader = new Unserialize_Reader_ArrValue('data');
         $prevChar = null;
         for ($i = 0; $i < strlen($str); $i++) {
diff --git a/app/code/core/Mage/Sales/Model/Quote/Address.php b/app/code/core/Mage/Sales/Model/Quote/Address.php
index b3ca22dc0b2..7acfd689fc0 100644
--- a/app/code/core/Mage/Sales/Model/Quote/Address.php
+++ b/app/code/core/Mage/Sales/Model/Quote/Address.php
@@ -1167,8 +1167,12 @@ public function validateMinimumAmount()
      */
     public function getAppliedTaxes()
     {
+        $tax = $this->getData('applied_taxes');
+        if (empty($tax)) {
+            return [];
+        }
         try {
-            $return = Mage::helper('core/unserializeArray')->unserialize($this->getData('applied_taxes'));
+            $return = Mage::helper('core/unserializeArray')->unserialize($tax);
         } catch (Exception $e) {
             $return = [];
         }