Replace conditional with a guard statement.

app/controllers/projects/forks_controller.rb

@@ -29,13 +29,10 @@ class Projects::ForksController < Projects::ApplicationController
   end
 
   def new
-    if current_user.nil?
-      authenticate_user!
-    else
+    return authenticate_user! unless current_user
     @namespaces = current_user.manageable_namespaces
     @namespaces.delete(@project.namespace)
   end
-  end
 
   def create
     namespace = Namespace.find(params[:namespace_key])