## AVL Tree help.

I just need some help figuring why I'm getting a NullPointerException where the "height" starts under the insert method. I posted the whole code before but some editing errors happened and if you wanna see the whole code again I can paste that in again but I just need help specifically on this.

I'm just getting an error beginning at "if(t.left().height() - t.right().height() == 2){"

Am I using this the wrong way? I feel like the way i'm coding that part to find the height of the left tree is incorrect.

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```
//constructor
public static class AvlTreeNode{
private int value;
private AvlTreeNode left;
private AvlTreeNode right;
private int height;

public AvlTreeNode(int value, AvlTreeNode left, AvlTreeNode right){
this.value = value;
this.left = null;
this.right = null;
height = 0;
}
public AvlTreeNode(int value){
this.value = value;
left = null;
right = null;
}

public AvlTreeNode left(){
return this.left;
}

public AvlTreeNode right(){
return this.right;
}

public int value(){
return this.value;
}
public int height(){
return this.height;
}
}
//method to insert a new node and number to a tree
public static AvlTreeNode insert(AvlTreeNode t, int x){
if(t == null){
t = new AvlTreeNode(x,null,null);
return t;
}else if(x < t.value()){
t.left = insert(t.left(), x);
}else if(x > t.value()){
t.right = insert(t.right(), x);
}
if(t.left().height() - t.right().height() == 2){
if(x < t.left.value()){
t = singleRotateWithLeft(t);
}
else if(x > t.left().value()){
t = doubleRotateWithLeft(t);
}
else if(x > t.value()){
t.right = insert(t.right(), x);
}
}
return t;
}```