Where is the error (C#)?

Question

Hello. Can somebody please help me find a bug in my program? I have a 3*3 table that is stored as cells with reference to the 4 cells that touch them. The cells are stored in a one dimensional array. After creating all needed cells, I itterate through the array and connect all neighboring cells with storing their reference in a variable that belongs to the other cell.
However when I try to print the table by using only the central cell and it's references to the other cells, I get the nullPoinerException, even when all references should be filled.

My table (and output of the code) should look like this:
X
O#O
X

And here is the code:
https://code.sololearn.com/cOVl8k7exqHf/?ref=app

Answer 1

I used your inputs listed in lines 11 to 20 and didn't get an exception so I'm guessing you found & fixed this.

Answer 2

Yea... i fixed it and forgot to write it here. Sorry for wasting your time.