Ever had one of those coding days where nothing makes sense — not even your own code? I ran into one of those recently. What started as a simple API tweak spiralled into a weird bug hunt that made me question reality, logic, and possibly the entire HTTP spec.

Let me share what happened. If you’ve ever used Ok() in ASP.NET Core and expected a JSON response, only to get a mysterious 204 No Content… you’re in the right place.

The Problem

I was updating a controller endpoint that fetches a user profile by ID. Nothing fancy. If the user was found, return it. If not, return a 404. Easy, right?

return Ok(user);

But something weird was happening.

When user was null, instead of getting a 200 OK with a body — or even a 404 Not Found — the response was a 204 No Content. No body. Just… silence.

On the client side, my app crashed trying to parse a response that wasn’t there. I stared at the debugger. I stared at Postman. I stared into the void. What was going on?

The Solution

Turns out, ASP.NET Core is trying to be clever. If you pass null to Ok(null), it doesn’t send a JSON body with null. It sends a 204 No Content, assuming you meant that.

The fix?

Don’t return Ok(null).

If there’s a chance the object is null, check it before calling Ok():

if (user == null)
{
    return NotFound();
}

return Ok(user);

Boom. Clients are happy again. JSON flows freely. Sanity is restored.

A Deeper Explanation

ASP.NET Core’s behavior is technically correct — Ok() with null signals “I have nothing to send.” So it sends… nothing. A 204.This behavior is baked into the framework. Here’s the relevant excerpt from the ASP.NET Core source code:

if (objectResult.Value == null && ...)
{
    httpContext.Response.StatusCode = 204;
    return;
}

Yup — if the value is null, it short-circuits and sends a 204.

You can also find this documented in the official ASP.NET Core return types and status codes docs:

“An action that returns an ObjectResult with a null value will produce a 204 No Content response.”

So this behavior is both intentional and consistent — just not always intuitive when you’re debugging.

Best Practices

• Always validate data before returning Ok().
• Use NotFound() explicitly if the object is null.
• Add unit tests to ensure your API responses match client expectations.
• Be cautious with nulls — ASP.NET Core has opinions.

Conclusion

This was a small bug with a surprisingly sneaky effect. But it reminded me how even “harmless” code like Ok() can behave in unexpected ways. If you’re scratching your head over a 204 No Content, double-check what you’re returning.

Stay curious. Keep debugging. And remember: sometimes the silence is the bug.