If a user has authorized their account but you no longer have a valid access_token for them, then a new one can be generated by using the refreshToken.
When your application receives a refresh token, it is important to store that refresh token for future use.
If your application loses the refresh token, you will have to prompt the user for their login information again.
/// Thrown when a null reference is passed to a method that does not accept it as a
/// valid argument.
/// Thrown when an error is found in a response from an Imgur endpoint. Thrown when an error is found in a response from a Mashape endpoint.