Create individual prefabs

Hi there,

I want to create a pointcloud. For this I have a Chunk class which can create voxel at any position. Because of the size of my cloud I have to seperate it into several chunks. Each chunk contains 8125 voxel. For this I created a world class where I instantiate a chunk and then I want to send it the coordiantes for the voxels. In someway it works and I can see two voxels but then I get "NullReferenceException: Object reference not set to an instance of an object" and I don't unterstand why. Here is my code:

From world script:

 public GameObject chunkPrefab;
 public GameObject newChunkObject;
 public void CreateChunk(Vector3[] coordinates)
     {
         newChunkObject = Instantiate(chunkPrefab, new Vector3(0,0,0), 
                              Quaternion.Euler(Vector3.zero)) as GameObject;
 
         Chunk newChunk = newChunkObject.GetComponent<Chunk>();
 
        newChunk.createBlockAt(0,0, 0);
     }
 

From chunk script:

 public virtual void createBlockAt(int x, int y, int z)
     {
         RenderMesh(Blockdata(x, y, z));  
     }
 
 private MeshData Blockdata(int x, int y, int z)
     {
         meshData.vertices.Add(new Vector3(x - 0.5f, y + 0.5f, z + 0.5f));
         meshData.vertices.Add(new Vector3(x + 0.5f, y + 0.5f, z + 0.5f));
         meshData.vertices.Add(new Vector3(x + 0.5f, y + 0.5f, z - 0.5f));
         meshData.vertices.Add(new Vector3(x - 0.5f, y + 0.5f, z - 0.5f));
 
         meshData.vertices.Add(new Vector3(x - 0.5f, y - 0.5f, z - 0.5f));
         meshData.vertices.Add(new Vector3(x + 0.5f, y - 0.5f, z - 0.5f));
         meshData.vertices.Add(new Vector3(x + 0.5f, y - 0.5f, z + 0.5f));
         meshData.vertices.Add(new Vector3(x - 0.5f, y - 0.5f, z + 0.5f));
 
         meshData.AddQuadTriangles();
         
         return meshData;
     }
 
 private void RenderMesh(MeshData meshData)
     {
         filter.mesh.Clear();
         filter.mesh.vertices = meshData.vertices.ToArray();
         filter.mesh.triangles = meshData.triangles.ToArray();
         filter.mesh.RecalculateNormals()
    }

the error always ends in RenderMesh method.

I Also tried to send my chunk along with the methods but nothing changed. Hope someone can help me. Thank you.

EDIT: My prefab contains a script which creates individual meshes. I can change the mesh by individual coordinates.