$['pull_request'].head.repo.description can be null.

Author: iphydf

src/GitHub/Types/Base/Repository.hs

@@ -30,7 +30,7 @@ data Repository = Repository
     , repositoryCreatedAt        :: DateTime
     , repositoryDefaultBranch    :: Text
     , repositoryDeploymentsUrl   :: Text
-    , repositoryDescription      :: Text
+    , repositoryDescription      :: Maybe Text
     , repositoryDownloadsUrl     :: Text
     , repositoryEventsUrl        :: Text
     , repositoryFork             :: Bool