changed return null to return false in mysqli driver if nothing was found

lib/Doctrine/DBAL/Driver/Mysqli/MysqliStatement.php

@@ -242,7 +242,7 @@ class MysqliStatement implements \IteratorAggregate, Statement
     {
         $values = $this->_fetch();
         if (null === $values) {
-            return null;
+            return false;
         }
 
         if (false === $values) {
@@ -292,7 +292,7 @@ class MysqliStatement implements \IteratorAggregate, Statement
                 $rows[] = $row;
             }
         } else {
-            while (($row = $this->fetch($fetchMode)) !== null) {
+            while (($row = $this->fetch($fetchMode)) !== false) {
                 $rows[] = $row;
             }
         }
@@ -306,7 +306,7 @@ class MysqliStatement implements \IteratorAggregate, Statement
     public function fetchColumn($columnIndex = 0)
     {
         $row = $this->fetch(PDO::FETCH_NUM);
-        if (null === $row) {
+        if (false === $row) {
             return false;
         }