We get an error when running either queries or inserts. The following error that occurs is `NoMethodError: undefined method `dispatch' for nil:NilClass` originating here https://github.com/mongodb/mongo-ruby-driver/blob/v2.0.3/lib/mongo/operation/executable.rb#L35

This means that `nil` was yielded from `Mongo::Server::ConnectionPool#with_connection` which in turn must mean that `Mongo::Server::ConnectionPool::Queue#dequeue` can return `nil`.

Looking at the code it doesn't seem like this can happen unless some non-thread safe stuff is going on.

I will try different ruby versions, but at this point I cannot figure out what is causing this.