diff --git a/src/templates/core/fetch/getHeaders.hbs b/src/templates/core/fetch/getHeaders.hbs
index 3d1a62c7..6808661f 100644
--- a/src/templates/core/fetch/getHeaders.hbs
+++ b/src/templates/core/fetch/getHeaders.hbs
@@ -2,13 +2,20 @@ async function getHeaders(options: ApiRequestOptions): Promise<Headers> {
     const token = await resolve(options, OpenAPI.TOKEN);
     const username = await resolve(options, OpenAPI.USERNAME);
     const password = await resolve(options, OpenAPI.PASSWORD);
-    const defaultHeaders = await resolve(options, OpenAPI.HEADERS);
+    const additionalHeaders = await resolve(options, OpenAPI.HEADERS);
 
-    const headers = new Headers({
+    const defaultHeaders = Object.entries({
         Accept: 'application/json',
-        ...defaultHeaders,
+        ...additionalHeaders,
         ...options.headers,
-    });
+    })
+        .filter(([key, value]) => isDefined(value))
+        .reduce((headers, [key, value]) => ({
+            ...headers,
+            [key]: value,
+        }), {});
+
+    const headers = new Headers(defaultHeaders);
 
     if (isStringWithValue(token)) {
         headers.append('Authorization', `Bearer ${token}`);
diff --git a/src/templates/core/node/getHeaders.hbs b/src/templates/core/node/getHeaders.hbs
index fc6d5516..040ef27a 100644
--- a/src/templates/core/node/getHeaders.hbs
+++ b/src/templates/core/node/getHeaders.hbs
@@ -2,13 +2,20 @@ async function getHeaders(options: ApiRequestOptions): Promise<Headers> {
     const token = await resolve(options, OpenAPI.TOKEN);
     const username = await resolve(options, OpenAPI.USERNAME);
     const password = await resolve(options, OpenAPI.PASSWORD);
-    const defaultHeaders = await resolve(options, OpenAPI.HEADERS);
+    const additionalHeaders = await resolve(options, OpenAPI.HEADERS);
 
-    const headers = new Headers({
+    const defaultHeaders = Object.entries({
         Accept: 'application/json',
-        ...defaultHeaders,
+        ...additionalHeaders,
         ...options.headers,
-    });
+    })
+        .filter(([key, value]) => isDefined(value))
+        .reduce((headers, [key, value]) => ({
+            ...headers,
+            [key]: value,
+        }), {});
+
+    const headers = new Headers(defaultHeaders);
 
     if (isStringWithValue(token)) {
         headers.append('Authorization', `Bearer ${token}`);
diff --git a/src/templates/core/xhr/getHeaders.hbs b/src/templates/core/xhr/getHeaders.hbs
index 3d1a62c7..6808661f 100644
--- a/src/templates/core/xhr/getHeaders.hbs
+++ b/src/templates/core/xhr/getHeaders.hbs
@@ -2,13 +2,20 @@ async function getHeaders(options: ApiRequestOptions): Promise<Headers> {
     const token = await resolve(options, OpenAPI.TOKEN);
     const username = await resolve(options, OpenAPI.USERNAME);
     const password = await resolve(options, OpenAPI.PASSWORD);
-    const defaultHeaders = await resolve(options, OpenAPI.HEADERS);
+    const additionalHeaders = await resolve(options, OpenAPI.HEADERS);
 
-    const headers = new Headers({
+    const defaultHeaders = Object.entries({
         Accept: 'application/json',
-        ...defaultHeaders,
+        ...additionalHeaders,
         ...options.headers,
-    });
+    })
+        .filter(([key, value]) => isDefined(value))
+        .reduce((headers, [key, value]) => ({
+            ...headers,
+            [key]: value,
+        }), {});
+
+    const headers = new Headers(defaultHeaders);
 
     if (isStringWithValue(token)) {
         headers.append('Authorization', `Bearer ${token}`);
diff --git a/src/templates/core/xhr/getResponseBody.hbs b/src/templates/core/xhr/getResponseBody.hbs
index 1da88836..4dc29fb5 100644
--- a/src/templates/core/xhr/getResponseBody.hbs
+++ b/src/templates/core/xhr/getResponseBody.hbs
@@ -1,16 +1,18 @@
 function getResponseBody(xhr: XMLHttpRequest): any {
-    try {
-        const contentType = xhr.getResponseHeader('Content-Type');
-        if (contentType) {
-            const isJSON = contentType.toLowerCase().startsWith('application/json');
-            if (isJSON) {
-                return JSON.parse(xhr.responseText);
-            } else {
-                return xhr.responseText;
+    if (xhr.status !== 204) {
+        try {
+            const contentType = xhr.getResponseHeader('Content-Type');
+            if (contentType) {
+                const isJSON = contentType.toLowerCase().startsWith('application/json');
+                if (isJSON) {
+                    return JSON.parse(xhr.responseText);
+                } else {
+                    return xhr.responseText;
+                }
             }
+        } catch (error) {
+            console.error(error);
         }
-    } catch (error) {
-        console.error(error);
     }
     return null;
 }