From 7cb1626bdc5a57d8fd193ed9bcc4191d27525f12 Mon Sep 17 00:00:00 2001
From: Curious Crook <70259149+CuriousCrook@users.noreply.github.com>
Date: Mon, 27 Sep 2021 10:21:14 +0200
Subject: [PATCH] Fix crash if server does not provide DiscoveryUrls

The OPC UA specification does not forbid that a server does not offer DiscoveryUrls. This can lead to a crash when calling the function application_to_strings().

Check DiscoveryUrls for None or empty before iterating to avoid the crash described in #1127.
---
 opcua/tools.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/opcua/tools.py b/opcua/tools.py
index 889cd5fe6..cc93269eb 100644
--- a/opcua/tools.py
+++ b/opcua/tools.py
@@ -418,8 +418,9 @@ def application_to_strings(app):
     for (n, v) in optionals:
         if v:
             result.append((n, v))
-    for url in app.DiscoveryUrls:
-        result.append(('Discovery URL', url))
+    if app.DiscoveryUrls:
+        for url in app.DiscoveryUrls:
+            result.append(('Discovery URL', url))
     return result  # ['{}: {}'.format(n, v) for (n, v) in result]