Removing 1 item in a players inventory

I need help getting rid of 1 item in an inventory even if it is a stack just 1

 

Code:

int index = <inv>.first(<Material>));
ItemStack item = <inv>.getItem(index);
int amt = item.getAmount();
if(amt <= 1) {
    <inv>.setItem(index, null);
} else {
    item.setAmount(amt - 1);
}

 

First Thank you very much, it works but when the person doesn't have enough of the material it says

 

It's hard to do anything without seeing the error, but try

Code:

int index = <inv>.first(<Material>);
if(index >= 0) {
    ItemStack item = <inv>.getItem(index);
    int amt = item.getAmount();
    if(amt <= 1) {
        <inv>.setItem(index, null);
    } else {
        item.setAmount(amt - 1);
    }
}

 

getInventory().removeItem(new ItemStack(Material, 1));