diff --git a/nova/api/validation/validators.py b/nova/api/validation/validators.py
index f3c0c9d1a7..bfe98b1eeb 100644
--- a/nova/api/validation/validators.py
+++ b/nova/api/validation/validators.py
@@ -34,7 +34,7 @@ from nova.i18n import _
 
 @jsonschema.FormatChecker.cls_checks('regex')
 def _validate_regex_format(instance):
-    if not isinstance(instance, six.text_type):
+    if not instance or not isinstance(instance, six.text_type):
         return False
     try:
         re.compile(instance)
diff --git a/nova/tests/unit/api/openstack/compute/test_serversV21.py b/nova/tests/unit/api/openstack/compute/test_serversV21.py
index 634f2aee57..9c391116a7 100644
--- a/nova/tests/unit/api/openstack/compute/test_serversV21.py
+++ b/nova/tests/unit/api/openstack/compute/test_serversV21.py
@@ -702,6 +702,20 @@ class ServersControllerTest(ControllerTest):
         self.assertRaises(exception.ValidationError,
                           self.controller.index, req)
 
+    def test_get_servers_with_empty_regex_filter_param(self):
+        empty_string = ''
+        req = self.req('/fake/servers?flavor=%s' % empty_string,
+                       use_admin_context=True)
+        self.assertRaises(exception.ValidationError,
+                          self.controller.index, req)
+
+    def test_get_servers_detail_with_empty_regex_filter_param(self):
+        empty_string = ''
+        req = self.req('/fake/servers/detail?flavor=%s' % empty_string,
+                       use_admin_context=True)
+        self.assertRaises(exception.ValidationError,
+                          self.controller.detail, req)
+
     def test_get_servers_invalid_sort_key(self):
         req = self.req('/fake/servers?sort_key=foo&sort_dir=desc')
         self.assertRaises(exception.ValidationError,