ArgumentNullException appear randomly in Unitywebrequest

Hi everyone,

I'm posting here today because I have some weird issues using UnityWebRequests

I'm developing an app that requires getting some files over the Internet. In order to get those files I use UnityWebRequests and a FileStream to download everything locally, but sometimes I have issues with some files that stop being downloaded (while some others are being downloaded entirely), when I look with my debugger, I discover that many fields in my UnityWebRequest have the same exception :

Code (CSharp):

1. System.ArgumentNullException : Value cannot be null.
2. Parameter name: _unity_self

Does anyone know where that could come from?

Thanks a lot

 

You could try and simplify the problem. Create a new scene and add into it only the download script (give some hardcoded filenames etc. just to make it run). Can you reproduce the problem that way?

If not, then maybe something else in the real scene is causing the problem. If it is repeatable, then try posting that cut-down code here. It may help others to see what is happening.

 

Did you find a solution to this? I'm having it as well.

 

I didn't find a solution so I went with another way to download my files (using WebClient and async methods)

 

I've been getting this too, in 2018.2 and also in 2018.3.0b5, its a real bummer. I was hoping the new web requests would be nice and robust... does anyone know of a work-around? My old code used WWW, but since that was obsoleted I switched to UnityWebRequest, is WebClient fast and full cross platform?

 

me too！

 

Thanks for the response, I solved the problem by having less concurrent downloads. I was downloading ~100 small files simultaneously, and it seems that it did not like doing that. Maybe it has to do with available system resources prohibiting having too many files open being written to simultaneously, and not unity code?

 

Having exactly the same problem, periodically doing UnityWebRequest, after a while it fails with timeout and the game has to be restarted as making any new requests causes:

Code (CSharp):

1. System.ArgumentNullException : Value cannot be null.
2. Parameter name: _unity_self

Happening on Unity 2019.1.9f

 

Thanks, yes, that was the cause.

 

There's also a Unity bug that could be causing this: https://issuetracker.unity3d.com/is...rown-when-yielding-and-disposing-a-www-object.

 

I would like to update the topic, the bug still exist in 2018.4.1:

Code (CSharp):

1.     if (uwr != null) {
2.       if (!uwr.isDone)
3.         uwr.Abort();
4.       uwr.Dispose();
5.     }

Despite that I am checking that uwr is not null and not done, I am still getting ArgumentNullException: Value cannot be null. So seems like that uwr gets disposed in another thread (coroutine) by using () {} construction.

When I did some experiments, calling only Dispose() also aborts the download process. To be 100% sure that download will be aborted and no exception will be invoked, I used try {} except ().

I hope this information will be helpful for someone.

 

@Aurimas-Cernius thanks for your answer. I was expecting that using() {} construction not only calls Dispose() method but also nulls variable. Thanks!

 

very helpful explanation @Aurimas-Cernius , I was disposing after isnetworkerror was true and reusing UWR obj. thanks!

 

The exception that is thrown when a C# null reference is passed to a method that does not accept it as a valid argument. An ArgumentNullException exception is thrown at run time in the following two major circumstances:

• An uninstantiated object is passed to a method. To prevent the error, instantiate the object.

• An object returned from a method call is then passed as an argument to a second method, but the value of the original returned object is null. To prevent the error, check for a return value that is null and call the second method only if the return value is not null.