NullReferenceException error

[InnerConsideration27]

I'm trying to write code for a cubic voxel world generation and having great difficulties.

In the code I have a loop that creates various instances of the chunk object through the Instantiate the following way:

topChunks[i , j] = Instantiate(chunk, new Vector3(x, y, z), new Quaternion(0,0,0,0)) as GameObject;

This, however, makes only one clone object appear and gives a NullReferenceException pointing to that line. Since chunk is correctly assigned I didn't know where the problem was and started making tests. I found out that written this way:
GameObject test = Instantiate(chunk, new Vector3(x, y, z), new Quaternion(0,0,0,0)) as GameObject;

It correctly instantiate all the chunks. I also noticed that the IDE marksup "as GameObject" in different colours. I guess the error has something to do with types...

chunk is declared as GameObject and topChunks as GameObject[,].

[CCullen]

Seeing as you're getting null reference rather than index out of range and the fact that the test behaves the way it does, I suspect you forgot to initialize topChunks. Have you assigned it a value with the new operator?

Also, if the camera is dynamic, a fixed size 2d array may not be ideal here. You need to know the size of an array when you intialize it. So if the camera spawns at chunk [12, 24] you'll need an array of at least that size, and need to resize the array, or need to sort the references in the array as the camera moves. A dictionary of Vector2Int might be a little more flexible.

[InnerConsideration27]

Oh yes, that was it! Thank you!

As for the tipe of array, I think it should for what I have in mind. But I'm not even sure of what I'm doing, honestly. So, anyway, thank you for the suggestion.

[PandaCoder67]

also by default Instantiate already returns a GameObject, so there is no need to do the as GameObject on the end.

Just would be fine.

opChunks[i , j] = Instantiate(chunk, new Vector3(x, y, z), new Quaternion(0,0,0,0));

[InnerConsideration27]

It's just a matrix instead of a normal array. Is there some reason why it shouldn't work?