Trying to get property of non-object - laravel - laravel

Question

I am tring to do now is to make a many to many relation between "payments" table and "invoices" table ... but my problem is when i try to add a new payment and i select e list of invoices laravel gives me " Trying to get property of non-object " in line 217 ..
this is my code :
$selectedInvoices = $input['invoice'];
$invoices = collect([]);
foreach ($selectedInvoices as $invoice) {
$invoices = $invoices->merge([Invoice::find(Invoice::getPrivateId($invoice))]);
}
$invoices->all();
$invoices = $invoices->sortByDesc(function($invoice)
{
return $invoice->invoice_date;
});
$invoices->values()->all();
$totalAmount = 0;
foreach ($invoices as $invoice)
{
$totalAmount = $totalAmount + $invoice->balance;
}
if($payment->amount > $totalAmount){
foreach ($invoices as $invoice){
$adjustment = $invoice->balance * -1;
$partial = max(0, $invoice->partial - 0);
$invoice->updateBalances($adjustment, $partial);
$invoice->updatePaidStatus();
$payment->invoices()->attach($invoice->id) ;
}
$credit = Credit::createNew();
$credit->client_id = $clientId;
$credit->amount = $payment->amount - $totalAmount ;
$credit->balance = $payment->amount - $totalAmount ;
$credit->credit_date = $payment->payment_date;
$credit->private_notes = 'Crédit créé automatiquement suite au payement '.$payment->id.
' avec un montant de '.$payment->amount.' à la date de '.$payment->payment_date;
$credit->save();
}
if($payment->amount <= $totalAmount)
{
/*line 217*/ while ($payment->amount >= $invoices->last()->balance){
$payment->amount = $payment->amount - $invoices->last()->balance ;
$adjustment = $invoices->last()->balance * -1;
$partial = max(0, $invoices->last()->partial - 0);
$invoices->last()->updateBalances($adjustment, $partial);
$invoices->last()->updatePaidStatus();
$payment->invoices()->attach($invoices->last()->id) ;
$invoices->pop();
$invoices->all();
}
if ($payment->amount < $invoices->last()->balance){
$adjustment = $payment->amount * -1;
$partial = max(0, $invoices->last()->partial - $payment->amount);
$invoices->last()->updateBalances($adjustment, $partial);
$invoices->last()->updatePaidStatus();
$payment->invoices()->attach($invoices->last()->id) ;
}
}
p.s: when i give an amount > total amount of my invoices it works also when i give an amount < total amount it works too ..

Answer 1

Switch line 217
From:
while ($payment->amount >= $invoices->last()->balance){
To:
while (count($invoices) && $payment->amount >= $invoices->last()->balance) {
Explanation: $invoices->pop() is removing the last item in the collection. When all the items have been removed from the invoices collection, no invoice object will be found; Hence, the Trying to get property of non-object