diff --git a/CMakeLists.txt b/CMakeLists.txt
index f737425..ada646e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,7 +6,7 @@ if(${CMAKE_VERSION} VERSION_LESS 3.12)
 endif()
 
 project(gitea2rss
-  VERSION 0.5.0
+  VERSION 0.5.1
   LANGUAGES CXX)
 
 # DESCRIPTION was introduced in version 3.9.
diff --git a/src/main.cpp b/src/main.cpp
index 80e852f..6cd0f5f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -30,7 +30,7 @@ using Poco::Environment;
 
 int main(int argc, char *argv[])
 {
-    const string query = Environment::get("QUERY_STRING");
+    const string query = Environment::get("QUERY_STRING", "");
     string url;
     string type = "releases";
 
@@ -40,7 +40,7 @@ int main(int argc, char *argv[])
 
     if (!query.empty())
     {
-        const string baseurl = Environment::get("GITEA2RSS_BASEURL");
+        const string baseurl = Environment::get("GITEA2RSS_BASEURL", "");
         if (baseurl.empty())
         {
             cout << "Status: 500 Internal Server Error\n\n";
diff --git a/src/write.cpp b/src/write.cpp
index 541be20..d1e333a 100644
--- a/src/write.cpp
+++ b/src/write.cpp
@@ -44,9 +44,9 @@ void write_line(const uint8_t spaces, const string &tag, const string &value)
 
 void write_preamble(const string &url, const string &type)
 {
-    const string request_uri = Environment::get("REQUEST_URI");
-    const string server_name = Environment::get("SERVER_NAME");
-    const string https = Environment::get("HTTPS");
+    const string request_uri = Environment::get("REQUEST_URI", "");
+    const string server_name = Environment::get("SERVER_NAME", "");
+    const string https = Environment::get("HTTPS", "");
     string selfurl;
 
     if (!request_uri.empty() && !server_name.empty())