As reported in https://jira.mongodb.org/browse/MONGOID-5306, when MissingAttributeError is raised, it does not report which model class was referenced:

serene2% mongoid=master rake test_5306
rake aborted!
ActiveModel::MissingAttributeError: Missing attribute: 'address'

          raise ActiveModel::MissingAttributeError, "Missing attribute: '#{field_name}'"

To make troubleshooting easier the exception should specify at least the model class (and possibly an inspection of the model truncated to some reasonable length).