Fix Ruby warning: instance variable not initialized
Fix Ruby warning: instance variable not initialized

[progress #799]

nbulaj/doorkeeper,nbulaj/doorkeeper,jasl/doorkeeper,mavenlink/doorkeeper,doorkeeper-gem/doorkeeper,mavenlink/doorkeeper,jasl/doorkeeper,outstand/doorkeeper,dollarshaveclub/doorkeeper,jasl/doorkeeper,moneytree/doorkeeper,doorkeeper-gem/doorkeeper,outstand/doorkeeper,doorkeeper-gem/doorkeeper,outstand/doorkeeper,moneytree/doorkeeper,EasterAndJay/doorkeeper,EasterAndJay/doorkeeper,mavenlink/doorkeeper,dollarshaveclub/doorkeeper