String-Array toCharArray broken?

I just encountered some strange behavior.
I am creating a string[], each index containing 16x '0'. Then I want to change that char to a different type as a spawning list.
I run the script. And got an nullpointer exception. So I started debugging. I do not understand how this is happening:
Note: I switched to .net 4.5 in Unity, is this causing it?

Code (CSharp):

1.         spawnList = new string[val.level * 2 + 10];
2.         for (int i = 0; i < spawnList.Length; i++) {
3.             for (int j = 0; j < 16; j++) {
4.                 spawnList[i] += "0";
5.             }
6.         }
7.         char[] tmp;
8.         int badLuck = 10;
9.         int count = 1;
10.         while (maxCoins > 0) {
11.             int start = Random.Range(1, 4);
12.             int step = Random.Range(1, 4);
13.             for (int i = start; i < val.level * 2 + 10; i += step) {
14.                 for (int j = 0; j < 16; j++) {
15.                     Debug.Log(i + " " + j + " " + spawnList[i] +  "  " + spawnList[i][j]);
16.                      [......]

It created this output:


I also tryed

Debug.Log(i + " " + j + " " + spawnList[i] +  "  " + spawnList[i][j]);

Debug.Log(i + " " + j + " " + spawnList[i] +  "  " + spawnList[i].toCharArray()[j]);

Debug.Log(i + " " + j + " " + spawnList[i].toString() +  "  " + spawnList[i].toCharArray()[j].toString());

 

The problem is probably in the part you didn't list.

 

Yea... I just discoverd that a char[] var with .toString() will in fact return System.Char[] and not the char[] as string...

Had:

Code (CSharp):

1. char[] tmp = spawnList[i].ToCharArray();
2. tmp[j] = 'g';
3. spawnList[i] = tmp.toString();

Correct:

Code (CSharp):

1. char[] tmp = spawnList[i].ToCharArray();
2. tmp[j] = 'g';
3. spawnList[i] = new string(tmp);

 

Code (csharp):

1. char[] bar = new char[10];
2. var baz = bar.ToString();
3. Debug.Log(baz.GetType());

prints out System.String.