In mongodb/laravel-mongodb 4.7;
In the builder.php script there is an upsert class that seem to be failing. looping over an array twice, seem like in some cases the array value is not an array, maybe there are some checking conditions that needs to be done.
i simply just return 0 if $values is true to make it work since i am not going to use upsert mutation
to replicate this issue write a simple graphql query try to test it you will see the error.