Initialize @trusted_proxies.

actionpack/test/dispatch/request_test.rb

@@ -474,6 +474,7 @@ protected
 
   def stub_request(env = {})
     ip_spoofing_check = env.key?(:ip_spoofing_check) ? env.delete(:ip_spoofing_check) : true
+    @trusted_proxies ||= nil
     ip_app = ActionDispatch::RemoteIp.new(Proc.new { }, ip_spoofing_check, @trusted_proxies)
     tld_length = env.key?(:tld_length) ? env.delete(:tld_length) : 1
     ip_app.call(env)