Object reference not set to an instance at Compilation step ?

Hi all

I have a compilation error with the (simplified) following code, and I have no idea how to remove it. First, the error :

 NullReferenceException: Object reference not set to an instance of an object 
 ManagementData+Data.GetMaxAmo () (at Assets/Player/Script.cs:xx)
 ManagementData+Data..ctor () (at Assets/Scripts/Script.cs:yy)
 ManagementData..ctor () (at Assets/Scripts/Script.cs:zz)

 NullReferenceException: Object reference not set to an instance of an object 
 ManagementData+Data.GetMaxAmo () (at Assets/Player/Script.cs:xx)
 ManagementData+Data..ctor () (at Assets/Scripts/Script.cs:yy)

I precise that the project runs without error.

Here is the code

 public class Management : MonoBehaviour
 {
     public static Management Instance;
     public ManagementData md;
 
     void Awake()
     {
         if (Instance == null) {
             Instance = this;
             md = new ManagementData ();
         }
     }
 }
 
 
 [Serializable]
 public class ManagementData
 {
     public Data data;
 
     public ManagementData()
     {
         data = new Data ();
     }
 
     public int Method1()
     {
         return 0;
     }
 }
 
 
 [Serializable]
 public class Data
 {
     protected int value;
 
     public Data()
     {
         value = Method2 ();
     }
 
     public int Method2()
     {
         return Management.Instance.md.Method1();
     }
 }

The line Assets/Scripts/Script.cs:xx refers to the following

return Management.Instance.md.Method1();

The line Assets/Scripts/Script.cs:yy refers to the following

value = Method2 ();

The line Assets/Scripts/Script.cs:zz refers to the following

data = new Data ();

Of course, all the attributes are well instantiated, and I repeat that there is no problem with the execution, just with the compilation step.

I noticed that if I remove the [Serializable] of the class Data, the second error disappears. If I remove also the [Serializable] of the class ManagementData, all the errors disappear.

I hope I've exposed well the situation.

Brett