Do not try to quote null value for SQL

Core/Frameworks/Flake/Core/Database.php

@@ -178,9 +178,13 @@ abstract class Database extends \Flake\Core\FLObject {
 
         foreach ($arr as $k => $v) {
             if ($noQuote === false || !in_array($k, $noQuote)) {
+                if ($v === null) {
+                    $arr[$k] = "NULL";
+                } else {
                     $arr[$k] = $this->fullQuote($v, $table);
                 }
             }
+        }
 
         return $arr;
     }