fix: Fixed issue where file parameter object is incorrectly JSON serialised

Author: BottlecapDave

modules/openapi-generator/src/main/resources/csharp/libraries/generichost/api.mustache

@@ -559,19 +559,69 @@ namespace {{packageName}}.{{apiPackage}}
                     {{/formParams}}
                     {{#bodyParam}}
                     {{#required}}
-                    httpRequestMessageLocalVar.Content = ({{paramName}}{{^required}}.Value{{/required}} as object) is System.IO.Stream stream
-                        ? httpRequestMessageLocalVar.Content = new StreamContent(stream)
-                        : httpRequestMessageLocalVar.Content = new StringContent(JsonSerializer.Serialize({{paramName}}{{^required}}.Value{{/required}}, _jsonSerializerOptions));
+                    if (({{paramName}}{{^required}}.Value{{/required}} as object) is System.IO.Stream stream)
+                    {
+                      httpRequestMessageLocalVar.Content = new StreamContent(stream);
+                    }
+                    {{#isFile}}
+                    else if (({{paramName}}{{^required}}.Value{{/required}} as object) is {{packageName}}.{{clientPackage}}.FileParameter fileParameterLocalVar)
+                    {
+                      httpRequestMessageLocalVar.Content = new StreamContent(fileParameterLocalVar.Content);
+                    }
+                    {{/isFile}}
+                    else
+                    {
+                      httpRequestMessageLocalVar.Content = new StringContent(JsonSerializer.Serialize({{paramName}}{{^required}}.Value{{/required}}, _jsonSerializerOptions));
+                    }
                     {{/required}}
                     {{^required}}
                     if ({{paramName}}.IsSet)
-                        httpRequestMessageLocalVar.Content = ({{paramName}}{{^required}}.Value{{/required}} as object) is System.IO.Stream stream
-                            ? httpRequestMessageLocalVar.Content = new StreamContent(stream)
-                            : httpRequestMessageLocalVar.Content = new StringContent(JsonSerializer.Serialize({{paramName}}{{^required}}.Value{{/required}}, _jsonSerializerOptions));
+                    {
+                      if (({{paramName}}{{^required}}.Value{{/required}} as object) is System.IO.Stream stream)
+                      {
+                        httpRequestMessageLocalVar.Content = new StreamContent(stream);
+                      }
+                      {{#isFile}}
+                      else if (({{paramName}}{{^required}}.Value{{/required}} as object) is {{packageName}}.{{clientPackage}}.FileParameter fileParameterLocalVar)
+                      {
+                        httpRequestMessageLocalVar.Content = new StreamContent(fileParameterLocalVar.Content);
+                      }
+                      {{/isFile}}
+                      else
+                      {
+                        httpRequestMessageLocalVar.Content = new StringContent(JsonSerializer.Serialize({{paramName}}{{^required}}.Value{{/required}}, _jsonSerializerOptions));
+                      }
+                    }
                     {{/required}}
 
                     {{/bodyParam}}
 
+                    {{#constantParams}}
+                    {{#isHeaderParam}}
+                    // Set client side default value of Header Param "{{baseName}}".                    
+                    if (_contentHeaders.Contains("{{baseName}}".ToLowerInvariant()))
+                    {
+                        httpRequestMessageLocalVar.Content.Headers.Add("{{baseName}}", ClientUtils.ParameterToString({{#_enum}}"{{{.}}}"{{/_enum}})); // Constant header parameter
+                    }
+                    else
+                    {
+                        httpRequestMessageLocalVar.Headers.Add("{{baseName}}", ClientUtils.ParameterToString({{#_enum}}"{{{.}}}"{{/_enum}})); // Constant header parameter
+                    }
+
+                    {{/isHeaderParam}}
+                    {{/constantParams}}
+                    {{#headerParams}}
+                    {{#required}}
+                    // Set client side default value of Header Param "{{baseName}}".                    
+                    if (_contentHeaders.Contains("{{baseName}}".ToLowerInvariant()))
+                    {
+                        httpRequestMessageLocalVar.Content.Headers.Add("{{baseName}}", ClientUtils.ParameterToString({{paramName}}));
+                    }
+                    else
+                    {
+                        httpRequestMessageLocalVar.Headers.Add("{{baseName}}", ClientUtils.ParameterToString({{paramName}}));
+                    }
+
                     {{/required}}
                     {{^required}}
                     if ({{paramName}}.IsSet)