mongo-php-driver: BulkWrite error :: '$set' is empty. You must specify a field like so: {$set: {: ...}}

Hey,

We recently switched our production server to PHP7:

$ php -v
PHP 7.0.4-7+deb.sury.org~trusty+2 (cli) ( NTS )
Copyright (c) 1997-2016 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2016 Zend Technologies
    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies

And using the new Mongodb driver (1.1.5).

We noticed that sometimes there’s a weird behaviour but unfortunately I can’t reproduce it yet (it’s quite random but for sure happens only on PHP7 servers). When I run the code on dev it works perfectly. I am seeing the following error:

BulkWrite error :: '$set' is empty. You must specify a field like so: {$set: {<field>: ...}}
app/vendor/composer/mongodb/mongodb/src/Operation/Update.php (121)
MongoDB\Driver\Server::executeBulkWrite


File:      app/vendor/composer//mongodb-odm-light/lib/Doctrine/MongoDB/Collection.php in line 1397
Method:    MongoCollection->update
Parameter: [['_id' => 'req-a10cd3c3-8485-4d21-9928-239379251472'], ['$set' => ['creatorHostname' => 'prod.cloud.net', 'handledAt' => MongoDate]], ['upsert' => true]]

File:      app/vendor/composer/alcaeus/mongo-php-adapter/lib/Mongo/MongoCollection.php in line 387
Method:    Alcaeus\MongoDbAdapter\ExceptionConverter::toLegacy
Parameter: [MongoDB\Driver\Exception\BulkWriteException]

As you can see, the $set parameter is definitely not empty. I have tried to debug a bit but still can’t figure this issue.

I am not sure if this bug should be here so I opened it also under mongo-php-adapter’s repository: https://github.com/alcaeus/mongo-php-adapter/issues/93

The moment I have a way to reproduce it, will attach a code snippet but maybe in the meanwhile there’s something I have missed.

Thank you