fix: undefined method `find_target' for nil (NoMethodError) #542

Author: route

lib/ferrum/contexts.rb

@@ -94,7 +94,7 @@ def subscribe # rubocop:disable Metrics/PerceivedComplexity
         add_context(context_id)
 
         if info["type"] == "iframe" &&
-           (target = @contexts[context_id].find_target { |t| t.connected? && t.page.frame_by(id: info["targetId"]) })
+           (target = @contexts[context_id]&.find_target { |t| t.connected? && t.page.frame_by(id: info["targetId"]) })
           @contexts[context_id]&.add_target(session_id: target.page.client.session_id, params: info)
         else
           @contexts[context_id]&.add_target(params: info)