In the present implementation `verifyUserRelations(Model)` assumes that
`Model.relations.accessTokens` is always set, and as a result may
crash when trying to access `polymorphic` property of that relation.
It seems the intention is to check whether the the following conditions
are met:
1. a model has a hasMany accessTokens relation
2. that relation is polymorphic
This commit fixes the problem by accounting for the case where the
accessTokens relation was not correctly set up.
9d77ba28d3