Avoid foreach errors.

Author: Carlos Cima

src/Model/Database.php

@@ -7,7 +7,7 @@ class Database
     /**
      * @var Table[]
      */
-    private $tables;
+    private $tables = [];
 
     /**
      * @return Table[]

src/Model/Table.php

@@ -32,7 +32,7 @@ class Table
     /**
      * @var Column[]
      */
-    private $primaryKeys;
+    private $primaryKeys = [];
 
     /**
      * @var ForeignKey[]