From 71edf641a5c94eaa2ca2ca09dcf5a9283f3df8bd Mon Sep 17 00:00:00 2001
From: Kenneth Hsu <kennethhsu@gmail.com>
Date: Sun, 27 Sep 2020 09:36:03 -0700
Subject: [PATCH] Avoid null reference exception when building Sia error
 messages.

If the resource does not provide an error response, the Response
property will be null.

This fixes #4193.
---
 Duplicati/Library/Backend/Sia/Sia.cs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Duplicati/Library/Backend/Sia/Sia.cs b/Duplicati/Library/Backend/Sia/Sia.cs
index 97aed2e7f..62db58a37 100644
--- a/Duplicati/Library/Backend/Sia/Sia.cs
+++ b/Duplicati/Library/Backend/Sia/Sia.cs
@@ -83,6 +83,11 @@ namespace Duplicati.Library.Backend.Sia
 
         private string getResponseBodyOnError(string context, System.Net.WebException wex)
         {
+            if (wex.Response is null)
+            {
+                return $"{context} failed with error: {wex.Message}";
+            }
+
             string body = "";
             System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)wex.Response;
             using (System.IO.Stream data = response.GetResponseStream())