Test fixes after module+builder test extension

Admin/Install/db.json

@@ -37,7 +37,7 @@
             "exchange_version": {
                 "name": "exchange_version",
                 "type": "VARCHAR(50)",
-                "null": null
+                "null": false
             }
         }
     }

Models/InterfaceManagerMapper.php

@@ -51,14 +51,6 @@ final class InterfaceManagerMapper extends DataMapperAbstract
      */
     protected static $table = 'exchange';
 
-    /**
-     * Created at.
-     *
-     * @var string
-     * @since 1.0.0
-     */
-    protected static $createdAt = 'exchange_created_at';
-
     /**
      * Primary field name.
      *