Adds operation null check avoid null exception (#15599)

* Adds operation null check in the method GetOperationServerUrl to avoid null exception

* Adds operation null check to avoid null exception to the csharp net core mustache

* update C# samples

---------

Co-authored-by: William Cheng <wing328hk@gmail.com>

modules/openapi-generator/src/main/resources/csharp-netcore/Configuration.mustache

@@ -544,7 +544,7 @@ namespace {{packageName}}.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/Configuration.cs

@@ -444,7 +444,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/Configuration.cs

@@ -569,7 +569,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/Configuration.cs

@@ -544,7 +544,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/Configuration.cs

@@ -574,7 +574,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClient-net48/src/Org.OpenAPITools/Client/Configuration.cs

@@ -574,7 +574,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/Configuration.cs

@@ -574,7 +574,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClient-unityWebRequest/src/Org.OpenAPITools/Client/Configuration.cs

@@ -544,7 +544,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/Configuration.cs

@@ -569,7 +569,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/Configuration.cs

@@ -574,7 +574,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }

samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/Configuration.cs

@@ -469,7 +469,7 @@ namespace Org.OpenAPITools.Client
         /// <return>The operation server URL.</return>
         public string GetOperationServerUrl(string operation, int index, Dictionary<string, string> inputVariables)
         {
-            if (OperationServers.TryGetValue(operation, out var operationServer))
+            if (operation != null && OperationServers.TryGetValue(operation, out var operationServer))
             {
                 return GetServerUrl(operationServer, index, inputVariables);
             }