Flag this error as a bad request.

module/VuFind/src/VuFind/Controller/CombinedController.php

@@ -251,7 +251,9 @@ class CombinedController extends AbstractSearch
                 return $this->redirect()->toRoute('home');
             }
             // If we have a weird value here, report it as an Exception:
-            throw new \Exception('Unexpected search type: "' . $type . '".');
+            throw new \VuFind\Exception\BadRequest(
+                'Unexpected search type: "' . $type . '".'
+            );
         }
     }
 

module/VuFind/src/VuFind/Exception/BadRequest.php

+<?php
+/**
+ * "Bad Request" Exception
+ *
+ * PHP version 5
+ *
+ * Copyright (C) Villanova University 2016.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * @category VuFind
+ * @package  Exceptions
+ * @author   Demian Katz <demian.katz@villanova.edu>
+ * @license  http://opensource.org/licenses/gpl-2.0.php GNU General Public License
+ * @link     https://vufind.org/wiki/development Wiki
+ */
+namespace VuFind\Exception;
+
+/**
+ * "Bad Request" Exception
+ *
+ * @category VuFind
+ * @package  Exceptions
+ * @author   Demian Katz <demian.katz@villanova.edu>
+ * @license  http://opensource.org/licenses/gpl-2.0.php GNU General Public License
+ * @link     https://vufind.org/wiki/development Wiki
+ */
+class BadRequest extends \Exception implements HttpStatusInterface
+{
+    /**
+     * Get HTTP status associated with this exception.
+     *
+     * @return int
+     */
+    public function getHttpStatus()
+    {
+        return 400;
+    }
+}