Fix crash in the flakiness dashboard server.

Tools/TestResultServer/model/datastorefile_test.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 39 matching lines @@
 
         self.assertTrue(self.test_file.save_data(test_data))
         self.assertEqual(test_data, self.test_file.data)
 
         self.assertEqual(test_data, self.test_file.load_data())
         self.assertEqual(test_data, self.test_file.data)
 
         self.test_file.delete_data()
         self.assertFalse(self.test_file.load_data())
 
+    def testLoadDataInvalidKey(self):
+        test_data = 'x' * datastorefile.MAX_ENTRY_LEN * 3
+
+        self.assertTrue(self.test_file.save_data(test_data))
+        self.assertEqual(test_data, self.test_file.data)
+
+        self.test_file.delete_data()
+        self.assertEqual('', self.test_file.load_data())
+
+    def testLoadDataNoKeys(self):
+        # This should never happen.
+        self.assertEqual(None, self.test_file.load_data())
+
     def testSaveData(self):
         self.assertFalse(self.test_file.save_data(None))
 
         too_big_data = 'x' * (datastorefile.MAX_DATA_ENTRY_PER_FILE * datastorefile.MAX_ENTRY_LEN + 1)
         self.assertFalse(self.test_file.save_data(too_big_data))
 
         test_data = 'x' * datastorefile.MAX_ENTRY_LEN * 5
         self.assertTrue(self.test_file.save_data(test_data))
         nchunks = datastorefile.DataEntry.all().count()
         nkeys = len(self.test_file.data_keys) + len(self.test_file.new_data_keys)
@@ skipping 24 matching lines @@
         self.assertEqual(len(chunk_indices), 3)
         self.assertNotEqual(chunk_indices[0], chunk_indices[-1])
 
         data_length += 1
         chunk_indices = self.test_file._get_chunk_indices(data_length)
         self.assertEqual(len(chunk_indices), 4)
 
 
 if __name__ == '__main__':
     unittest.main()