added empty check for raw_info email as well as nil

Author: khash

lib/omniauth/strategies/github.rb

@@ -48,7 +48,7 @@ def raw_info
       end
 
       def email
-        raw_info['email'] || primary_email
+        (raw_info['email'].nil? || raw_info['email'].empty?) || primary_email
       end
 
       def primary_email