Implement CR suggestions

Author: goce-cz

docs/openapi-fetch/api.md

@@ -188,8 +188,7 @@ for any request that provides value for the `body` parameter. When the `bodySeri
 `Content-Type` is omitted, allowing the browser to set it automatically with the correct message part boundary.
 
 You can also set `Content-Type` manually through `headers` object either in the fetch options,
-or when instantiating the client. Setting `Content-Type` to `null` will omit the header, however the native fetch API
-will likely set it to `text/plain` in this case.
+or when instantiating the client.
 
 :::
 

packages/openapi-fetch/test/index.test.ts

@@ -981,9 +981,10 @@ describe("client", () => {
             },
           });
           // the fetch implementation won't allow sending a body without content-type,
-          // so it invents one up and sends it, hopefully this will be consistent across
-          // local environments and won't make the tests flaky
-          expect(contentType).toBe("text/plain;charset=UTF-8");
+          // and it defaults to `text/plain;charset=UTF-8`, however the actual default value
+          // is irrelevant and might be flaky across different fetch implementations
+          // for us, it's important that it's not `application/json`
+          expect(contentType).not.toBe("application/json");
         },
       );