Error: Cannot read field "color" because "u" is null RED BLACK TREE

Question

Hello I have an assignment to implement a RBT tree and then as an application insert dictionary in it for more efficient insertion and searching operations. When I insert the dictionary file it only reads the first word and 2nd word but doesn't fix up the insertion of the 2nd word and this error shows up enter image description here when I debugged the problem is in the insertfixup method. I think that's where the u is but I'm not sure why even if I don't initialize u with anything it gives me the same error so I tried to initialize it with TNULL and it still the same I hope my problem is clear

private void insertFixUp(Node x) {
Node u = TNULL;
    while (x.parent.color == 1){
        if(x.parent == x.parent.parent.right){
            u=x.parent.parent.left;
        if (u.color == 1){
            u.color =0;
            x.parent.color = 0;
            x.parent.parent.color = 1;
            x = x.parent.parent;
        }
        else {
            if(x == x.parent.left) {
            x = x.parent;
            rightRotate(x);
        }
            x.parent.color=0;
            x.parent.parent.color=1;
            leftRotate(x.parent.parent);
        }
    } else {
            u = x.parent.parent.right;

            if (u.color == 1){
                u.color =0;
                x.parent.color = 0;
                x.parent.parent.color = 1;
                x = x.parent.parent;
            }
            else {
                if(x == x.parent.right) {
                    x = x.parent;
                    leftRotate(x);
                }
                x.parent.color=0;
                x.parent.parent.color=1;
                leftRotate(x.parent.parent);
            }
        }
        if(x == root){
            break;
        }
  }
    root.color=0;

}