fix for pure ruby encoder when _id is a falsey value. more tests

lib/mongo/util/bson.rb

@@ -86,13 +86,11 @@ class BSON
 
       # Write key/value pairs. Always write _id first if it exists.
       if obj.has_key? '_id'
-        oid = obj['_id']
+        serialize_key_value('_id', obj['_id'])
       elsif obj.has_key? :_id
-        oid = obj[:_id]
-      else
-        oid = false
+        serialize_key_value('_id', obj[:_id])
       end
-      serialize_key_value('_id', oid) if oid
+
       obj.each {|k, v| serialize_key_value(k, v) unless k == '_id' || k == :_id }
 
       serialize_eoo_element(@buf)

tests/test_bson.rb

@@ -181,6 +181,11 @@ class BSONTest < Test::Unit::TestCase
     assert_equal '_id', roundtrip.keys.first
   end
 
+  def test_nil_id
+    doc = {"_id" => nil}
+    assert_equal doc, @b.deserialize(@b.serialize(doc).to_a)
+  end
+
   def test_timestamp
     val = {"test" => [4, 20]}
     assert_equal val, @b.deserialize([0x13, 0x00, 0x00, 0x00,

tests/test_db_api.rb

@@ -547,14 +547,18 @@ class DBAPITest < Test::Unit::TestCase
     @@coll.clear
 
     assert_equal nil, @@db.dereference(DBRef.new("test", ObjectID.new))
-    obj = {"x" => true}
-    key = @@coll.insert(obj)["_id"]
-    assert_equal true, @@db.dereference(DBRef.new("test", key))["x"]
+    @@coll.insert({"x" => "hello"})
+    key = @@coll.find_first()["_id"]
+    assert_equal "hello", @@db.dereference(DBRef.new("test", key))["x"]
 
     assert_equal nil, @@db.dereference(DBRef.new("test", 4))
     obj = {"_id" => 4}
     @@coll.insert(obj)
     assert_equal obj, @@db.dereference(DBRef.new("test", 4))
+
+    @@coll.clear
+    @@coll.insert({"x" => "hello"})
+    assert_equal nil, @@db.dereference(DBRef.new("test", nil))
   end
 
 # TODO this test fails with error message "Undefed Before end of object"