GODRIVER-657 handle nil in EmptyInterfaceEncodeValue

Change-Id: Icaab6196e15f85c4b069c89116ef95891b9612d4

Author: Isabella Siu

bson/bsoncodec/default_value_encoders.go

@@ -444,6 +444,9 @@ func (dve DefaultValueEncoders) SliceEncodeValue(ec EncodeContext, vw bsonrw.Val
 
 // EmptyInterfaceEncodeValue is the ValueEncoderFunc for interface{}.
 func (dve DefaultValueEncoders) EmptyInterfaceEncodeValue(ec EncodeContext, vw bsonrw.ValueWriter, i interface{}) error {
+	if i == nil {
+		return vw.WriteNull()
+	}
 	encoder, err := ec.LookupEncoder(reflect.TypeOf(i))
 	if err != nil {
 		return err

bson/bsoncodec/default_value_encoders_test.go

@@ -430,6 +430,13 @@ func TestDefaultValueEncoders(t *testing.T) {
 				{"*[]byte/nil", pbytesliceNil, nil, nil, bsonrwtest.WriteNull, nil},
 			},
 		},
+		{
+			"EmptyInterfaceEncodeValue",
+			ValueEncoderFunc(dve.EmptyInterfaceEncodeValue),
+			[]subtest{
+				{"interface/nil", nil, nil, nil, bsonrwtest.WriteNull, nil},
+			},
+		},
 		{
 			"ValueMarshalerEncodeValue",
 			ValueEncoderFunc(dve.ValueMarshalerEncodeValue),