如何将多维原始数组转换为多维 object 数组

Question

I am trying to write code which will accept an integer array and convert the integers within it into keys of an object array of the same size. When I run it from the main method class, I keep getting null pointer exception.

In my main method, I have 5 grids (grid1,grid2...grid5) with data in the form of int [][]grid. In one of my classes, the constructor accepts a grid as a parameter and then calls the method createArrayFromArrayObject(int [][] grid), which is supposed to take the grid from the main method and then convert its integers into keys for the object method used by the constructor.

See below - I wrote the code together with where the error shows up. Calling the specific grids from main method of IDSearch: IDSearch ids = new IDSearch();

            SearchNode g1 = new SearchNode(grid1);
            SearchNode g2 = new SearchNode(grid2);
            SearchNode g3 = new SearchNode(grid3);
            SearchNode g4 = new SearchNode(grid4);
            SearchNode g5 = new SearchNode(grid5);

            ids.goalSearch(g1);//I get an error message here
            ids.goalSearch(g2);
            ids.goalSearch(g3);
            ids.goalSearch(g4);
            ids.goalSearch(g5);


SearchNode(int [][] grid){
    nodesMatrix = createArrayFromArrayObject(grid);//and then here
    for (int i=0; i<15; i++) { 
        for (int j=0; j<15; j++) {
            if(nodesMatrix[i][j].getElement() == 2) {
                xStart = i;
                yStart = j;
            }
            if(nodesMatrix[i][j].getElement()==3) {
                xGoal=i;
                yGoal=j;
etc.etc. 

public static Node [][] createArrayFromArrayObject(int [][] grid) {
    Node [][] nodesMatrix= new Node[15][15];
    for(int i = 0; i < grid.length; i++){
        for(int j = 0; j < grid.length; j++) {
            nodesMatrix[i][j].setElement(grid[i][j]);//and then here
        }
    }
    return nodesMatrix;
};
//and it throws a null pointer exception.

The error goes from the main method of IDSearch class to the constructor of SearchNode class to the create array from an array object method.

I am trying to figure out how to fix it so that it will access the grid data and will not throw a null pointer exception.