Don't save undefined atributes.

src/Libs/ModelMySQL.php

@@ -243,9 +243,11 @@ class ModelMySQL {
     $atts = $this->getVars();
     
     foreach ($atts as $key => $value) {
+      if (isset($value)) {
         $into[] = "`$key`";
         $values[] = "'".$db->real_escape_string($value)."'";
       }
+    }
     
     $table = static::table();
     $sql = "INSERT INTO $table (".join(', ', $into).") VALUES (".join(', ', $values).")";