diff --git a/modules/swagger-codegen/src/main/resources/TypeScript-Fetch/api.mustache b/modules/swagger-codegen/src/main/resources/TypeScript-Fetch/api.mustache
index deb227d02f..ad6e13e69b 100644
--- a/modules/swagger-codegen/src/main/resources/TypeScript-Fetch/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/TypeScript-Fetch/api.mustache
@@ -98,11 +98,12 @@ export const {{classname}}FetchParamCreator = {
             .replace(`{${"{{baseName}}"}}`, `${ params["{{paramName}}"] }`){{/pathParams}};
         let urlObj = url.parse(baseUrl, true);
 {{#hasQueryParams}}
-        urlObj.query = {{#supportsES6}}Object.{{/supportsES6}}assign({}, urlObj.query, {
-            {{#queryParams}}
-            "{{baseName}}": params["{{paramName}}"],
-            {{/queryParams}}
-        });
+        urlObj.query =  {{#supportsES6}}Object.{{/supportsES6}}assign({}, urlObj.query);
+    {{#queryParams}}
+        if (params["{{paramName}}"] !== undefined) {
+            urlObj.query["{{baseName}}"] = params["{{paramName}}"];
+        }
+    {{/queryParams}}
 {{/hasQueryParams}}
         let fetchOptions: RequestInit = {{#supportsES6}}Object.{{/supportsES6}}assign({}, { method: "{{httpMethod}}" }, options);
 
diff --git a/samples/client/petstore-security-test/typescript-fetch/api.ts b/samples/client/petstore-security-test/typescript-fetch/api.ts
index 4fe998131e..d4b0fbf3e8 100644
--- a/samples/client/petstore-security-test/typescript-fetch/api.ts
+++ b/samples/client/petstore-security-test/typescript-fetch/api.ts
@@ -71,7 +71,7 @@ export const FakeApiFetchParamCreator = {
             "test code inject */ ' " =end -- \r\n \n \r": params["test code inject * ' " =end  rn n r"],
         });
         if (contentTypeHeader) {
-            fetchOptions.headers = contentTypeHeader;
+            fetchOptions.headers = assign({}, contentTypeHeader, fetchOptions.headers);
         }
 
         return {
diff --git a/samples/client/petstore/typescript-fetch/builds/default/api.ts b/samples/client/petstore/typescript-fetch/builds/default/api.ts
index ffd2fc8ecc..378f912d8a 100644
--- a/samples/client/petstore/typescript-fetch/builds/default/api.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default/api.ts
@@ -200,9 +200,10 @@ export const PetApiFetchParamCreator = {
         }
         const baseUrl = `/pet/findByStatus`;
         let urlObj = url.parse(baseUrl, true);
-        urlObj.query = assign({}, urlObj.query, {
-            "status": params["status"],
-        });
+        urlObj.query =  assign({}, urlObj.query);
+        if (params["status"] !== undefined) {
+            urlObj.query["status"] = params["status"];
+        }
         let fetchOptions: RequestInit = assign({}, { method: "GET" }, options);
 
         let contentTypeHeader: Dictionary<string> = {};
@@ -234,9 +235,10 @@ export const PetApiFetchParamCreator = {
         }
         const baseUrl = `/pet/findByTags`;
         let urlObj = url.parse(baseUrl, true);
-        urlObj.query = assign({}, urlObj.query, {
-            "tags": params["tags"],
-        });
+        urlObj.query =  assign({}, urlObj.query);
+        if (params["tags"] !== undefined) {
+            urlObj.query["tags"] = params["tags"];
+        }
         let fetchOptions: RequestInit = assign({}, { method: "GET" }, options);
 
         let contentTypeHeader: Dictionary<string> = {};
@@ -1116,10 +1118,13 @@ export const UserApiFetchParamCreator = {
         }
         const baseUrl = `/user/login`;
         let urlObj = url.parse(baseUrl, true);
-        urlObj.query = assign({}, urlObj.query, {
-            "username": params["username"],
-            "password": params["password"],
-        });
+        urlObj.query =  assign({}, urlObj.query);
+        if (params["username"] !== undefined) {
+            urlObj.query["username"] = params["username"];
+        }
+        if (params["password"] !== undefined) {
+            urlObj.query["password"] = params["password"];
+        }
         let fetchOptions: RequestInit = assign({}, { method: "GET" }, options);
 
         let contentTypeHeader: Dictionary<string> = {};