Do not send Content-Type on file upload

frontend/app/common/fetcher.test.ts

@@ -146,10 +146,10 @@ describe('fetcher', () => {
         body: JSON.stringify(data),
       });
     });
-    it('should send form data', async () => {
+
+    it("shouldn't send content-type with form data", async () => {
       expect.assertions(1);
 
-      const headersWithMultipartData = { ...headers, 'Content-Type': 'multipart/form-data' };
       const body = new FormData();
 
       mockFetch();
@@ -158,7 +158,7 @@ describe('fetcher', () => {
       expect(window.fetch).toHaveBeenCalledWith(apiUrl, {
         method: 'post',
         body,
-        headers: headersWithMultipartData,
+        headers,
       });
     });
   });

frontend/app/common/fetcher.ts

@@ -48,7 +48,8 @@ const createFetcher = (baseUrl: string = ''): Methods => {
     headers[XSRF_HEADER] = getCookie(XSRF_COOKIE) || '';
 
     if (body instanceof FormData) {
-      headers['Content-Type'] = 'multipart/form-data';
+      // Shouldn't add any kind of `Content-Type` if we send `FormData`
+      // Now FormData is sent only in case of uploading file
       params.body = body;
     } else if (typeof body === 'object' && body !== null) {
       headers['Content-Type'] = 'application/json';