diff --git a/modules/openapi-generator/src/main/resources/csharp/Configuration.mustache b/modules/openapi-generator/src/main/resources/csharp/Configuration.mustache
index 069758033634..39dbd9c03943 100644
--- a/modules/openapi-generator/src/main/resources/csharp/Configuration.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/Configuration.mustache
@@ -603,7 +603,7 @@ namespace {{packageName}}.Client
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/echo_api/csharp/restsharp/net8/EchoApi/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/echo_api/csharp/restsharp/net8/EchoApi/src/Org.OpenAPITools/Client/Configuration.cs
index 5c8abc6ea702..13e61760f2b9 100644
--- a/samples/client/echo_api/csharp/restsharp/net8/EchoApi/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/echo_api/csharp/restsharp/net8/EchoApi/src/Org.OpenAPITools/Client/Configuration.cs
@@ -503,7 +503,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Client/Configuration.cs
index ffddac249d05..9a4b99cd8121 100644
--- a/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Client/Configuration.cs
@@ -497,7 +497,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/httpclient/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/httpclient/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index 02aefa69e18d..601dfdb2f3e7 100644
--- a/samples/client/petstore/csharp/httpclient/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/httpclient/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -602,7 +602,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/httpclient/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/httpclient/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index 08960c8389ea..ed3aecacd924 100644
--- a/samples/client/petstore/csharp/httpclient/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/httpclient/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -597,7 +597,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Configuration.cs
index d4177aa1d048..1176107c56fa 100644
--- a/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net4.7/MultipleFrameworks/src/Org.OpenAPITools/Client/Configuration.cs
@@ -528,7 +528,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index e104bdcf2770..e254dd2413ab 100644
--- a/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net4.7/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -633,7 +633,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index e104bdcf2770..e254dd2413ab 100644
--- a/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net4.8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -633,7 +633,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net8/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net8/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs
index 76aaeace6702..ccbe76060856 100644
--- a/samples/client/petstore/csharp/restsharp/net8/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net8/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs
@@ -633,7 +633,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net8/ParameterMappings/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net8/ParameterMappings/src/Org.OpenAPITools/Client/Configuration.cs
index edbaddee9a0d..d7146853e0f9 100644
--- a/samples/client/petstore/csharp/restsharp/net8/ParameterMappings/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net8/ParameterMappings/src/Org.OpenAPITools/Client/Configuration.cs
@@ -502,7 +502,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index 76aaeace6702..ccbe76060856 100644
--- a/samples/client/petstore/csharp/restsharp/net8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net8/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -633,7 +633,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/Configuration.cs
index 488b3d832e4e..5a7f7e948236 100644
--- a/samples/client/petstore/csharp/restsharp/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net8/UseDateTimeForDate/src/Org.OpenAPITools/Client/Configuration.cs
@@ -502,7 +502,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net8/useVirtualForHooks/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net8/useVirtualForHooks/src/Org.OpenAPITools/Client/Configuration.cs
index 35b89b430a80..c89eee968eca 100644
--- a/samples/client/petstore/csharp/restsharp/net8/useVirtualForHooks/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net8/useVirtualForHooks/src/Org.OpenAPITools/Client/Configuration.cs
@@ -533,7 +533,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/net9/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/net9/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs
index 76aaeace6702..ccbe76060856 100644
--- a/samples/client/petstore/csharp/restsharp/net9/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/net9/EnumMappings/src/Org.OpenAPITools/Client/Configuration.cs
@@ -633,7 +633,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Configuration.cs
index 18e94ac0845e..3ea2a481c169 100644
--- a/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/standard2.0/ConditionalSerialization/src/Org.OpenAPITools/Client/Configuration.cs
@@ -628,7 +628,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index 18e94ac0845e..3ea2a481c169 100644
--- a/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/restsharp/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -628,7 +628,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/unityWebRequest/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/unityWebRequest/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index 02aefa69e18d..601dfdb2f3e7 100644
--- a/samples/client/petstore/csharp/unityWebRequest/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/unityWebRequest/net9/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -602,7 +602,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }
diff --git a/samples/client/petstore/csharp/unityWebRequest/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs b/samples/client/petstore/csharp/unityWebRequest/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
index 08960c8389ea..ed3aecacd924 100644
--- a/samples/client/petstore/csharp/unityWebRequest/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/unityWebRequest/standard2.0/Petstore/src/Org.OpenAPITools/Client/Configuration.cs
@@ -597,7 +597,7 @@ private string GetServerUrl(IList<IReadOnlyDictionary<string, object>> servers,
 
                     if (inputVariables.ContainsKey(variable.Key))
                     {
-                        if (((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
+                        if (!serverVariables.ContainsKey("enum_values") || ((List<string>)serverVariables["enum_values"]).Contains(inputVariables[variable.Key]))
                         {
                             url = url.Replace("{" + variable.Key + "}", inputVariables[variable.Key]);
                         }