Null reference exception after add script

Hi. I have error about System.NullRefferenceException but it happen before run application.

The error log:
(0,0): error - System.NullReferenceException: Object reference not set to an instance of an object.|| at Unity.Netcode.Editor.CodeGen.INetworkSerializableILPP.Process(ICompiledAssembly compiledAssembly) in E:\Wanderland_Online\Library\PackageCache\com.unity.netcode.gameobjects@1.0.0-pre.9\Editor\CodeGen\INetworkSerializableILPP.cs:line 116 at Unity.Netcode.Editor.CodeGen.INetworkSerializableILPP.Process(ICompiledAssembly compiledAssembly) in E:\Wanderland_Online\Library\PackageCache\com.unity.netcode.gameobjects@1.0.0-pre.9\Editor\CodeGen\INetworkSerializableILPP.cs:line 116

And this script which I added

Code (CSharp):

1. using Unity.Netcode;
2. using UnityEngine;
3.  
4. public class Singleton<T> : NetworkBehaviour where T : Component
5. {
6.     static T _instance;
7.  
8.     public static T Instance
9.     {
10.         get
11.         {
12.             if (_instance != null)
13.                 return _instance;
14.  
15.             var objects = FindObjectsOfType(typeof(T));
16.             if (objects is T[] typeComponents)
17.             {
18.                 if (typeComponents.Length > 0)
19.                     _instance = typeComponents[0];
20.  
21.                 if (typeComponents.Length > 1)
22.                     Debug.LogError("More than one instance :" + typeof(T).Name + " exist in thr scene.");
23.             }
24.             else
25.             {
26.                 if (_instance == null)
27.                     _instance = new GameObject(typeof(T).Name).AddComponent<T>();
28.             }
29.  
30.             return _instance;
31.         }
32.     }
33. }
34.  

I can disable error if add unsafe before Singleton class but i dont want to do it. Also if remove

Code (CSharp):

1. where T: Component

error disappears from unity, but it is not what i want.

This code sample i found in this video:

Can anyone explain why it happens?

 

Have you fixed it? Im getting the same error

Edit: after downgrading from netcode1.0.0 pre 9 to 1.0.0 pre 6 the error went away and works perfectly

 

Sounds like you're making typos... don't do that!

I'm gonna guess you weren't supposed to type 'Scripts' wherever you typed it.

Remember: NOBODY here memorizes error codes. That's not a thing. The error code is absolutely the least useful part of the error. It serves no purpose at all. Forget the error code. Put it out of your mind.

The complete error message contains everything you need to know to fix the error yourself.

The important parts of the error message are:

- the description of the error itself (google this; you are NEVER the first one!)
- the file it occurred in (critical!)
- the line number and character position (the two numbers in parentheses)
- also possibly useful is the stack trace (all the lines of text in the lower console window)

Always start with the FIRST error in the console window, as sometimes that error causes or compounds some or all of the subsequent errors. Often the error will be immediately prior to the indicated line, so make sure to check there as well.

All of that information is in the actual error message and you must pay attention to it. Learn how to identify it instantly so you don't have to stop your progress and fiddle around with the forum.

Tutorials and example code are great, but keep this in mind to maximize your success and minimize your frustration:

How to do tutorials properly, two (2) simple steps to success:

Step 1. Follow the tutorial and do every single step of the tutorial 100% precisely the way it is shown. Even the slightest deviation (even a single character!) generally ends in disaster. That's how software engineering works. Every step must be taken, every single letter must be spelled, capitalized, punctuated and spaced (or not spaced) properly, literally NOTHING can be omitted or skipped.

Fortunately this is the easiest part to get right: Be a robot. Don't make any mistakes.
BE PERFECT IN EVERYTHING YOU DO HERE!!

If you get any errors, learn how to read the error code and fix your error. Google is your friend here. Do NOT continue until you fix your error. Your error will probably be somewhere near the parenthesis numbers (line and character position) in the file. It is almost CERTAINLY your typo causing the error, so look again and fix it.

Step 2. Go back and work through every part of the tutorial again, and this time explain it to your doggie. See how I am doing that in my avatar picture? If you have no dog, explain it to your house plant. If you are unable to explain any part of it, STOP. DO NOT PROCEED. Now go learn how that part works. Read the documentation on the functions involved. Go back to the tutorial and try to figure out WHY they did that. This is the part that takes a LOT of time when you are new. It might take days or weeks to work through a single 5-minute tutorial. Stick with it. You will learn.

Step 2 is the part everybody seems to miss. Without Step 2 you are simply a code-typing monkey and outside of the specific tutorial you did, you will be completely lost. If you want to learn, you MUST do Step 2.

Of course, all this presupposes no errors in the tutorial. For certain tutorial makers (like Unity, Brackeys, Imphenzia, Sebastian Lague) this is usually the case. For some other less-well-known content creators, this is less true. Read the comments on the video: did anyone have issues like you did? If there's an error, you will NEVER be the first guy to find it.

Beyond that, Step 3, 4, 5 and 6 become easy because you already understand!

 

How do I downgrade from netcode 1.0.0 pre 9 to 1.0.0 pre 6 in my own project? I have encountered a similar issue in a project I'm working on. Removing and reinstalling it forced me to use pre 9.

 

Correct me if I am wrong, but you should be able to modify the line

Code (csharp):

1. "com.unity.netcode.gameobjects": "1.0.0-pre.9"

to say

Code (CSharp):

1. "com.unity.netcode.gameobjects": "1.0.0-pre.6"

in manifest.json (in the packages folder of your project).

Hope this helps,
-Dguto9

 

Good news: While downgrading to pre6 reintroduced new compile errors, all problems were resolved by upgrading to pre-10. Yay!