Created unit test to check if a server error is raised in case no accessTokenExpiresAt is provided by model.
Created unit test to check if a server error is raised in case no accessTokenExpiresAt is provided by model.

razvanz/node-oauth2-server,thomseddon/node-oauth2-server,visvk/node-oauth2-server,mjsalinger/node-oauth2-server,oauthjs/node-oauth2-server