PYTHON-712 ObjectId.is_valid(None) should be False.

Author: ajdavis

bson/objectid.py

@@ -140,6 +140,9 @@ def is_valid(cls, oid):
 
         .. versionadded:: 2.3
         """
+        if not oid:
+            return False
+
         try:
             ObjectId(oid)
             return True

test/test_objectid.py

@@ -181,6 +181,7 @@ def test_pickle_backwards_compatability(self):
         self.assertEqual(oid_1_9, oid_1_10)
 
     def test_is_valid(self):
+        self.assertFalse(ObjectId.is_valid(None))
         self.assertFalse(ObjectId.is_valid(4))
         self.assertFalse(ObjectId.is_valid(175.0))
         self.assertFalse(ObjectId.is_valid({"test": 4}))