Getting Cannot use "::class" on null

I'm using FilamentPHP and have a resource with two tabs: "transactions" and "balances". The "transactions" tab works fine, but when I switch to the "balances" tab, I get the error:

Cannot use "::class" on null

namespace App\Filament\Resources\Operations\CollectionNetworkTransactionResource\Pages;

use App\Filament\Resources\Operations\CollectionNetworkTransactionResource; use Brick\Math\BigRational; use Filament\Actions; use Filament\Resources\Components\Tab; use Filament\Resources\Pages\ListRecords; use Filament\Tables\Columns\TextColumn; use Filament\Tables\Columns\Summarizers\Sum; use Filament\Tables\Table; use Illuminate\Database\Eloquent\Builder;

class ListCollectionNetworkTransaction extends ListRecords { protected static string $resource = CollectionNetworkTransactionResource::class;

protected function getHeaderActions(): array
{
    return [
        Actions\CreateAction::make(),
    ];
}

public function getTabs(): array
{
    return [
        'balances' => Tab::make(__('Balances'))
            ->icon('heroicon-o-chart-bar')
            ->query(fn (Builder $query) => $query), 

        'transactions' => Tab::make(__('Transactions'))
            ->icon('heroicon-o-chart-bar')
            ->query(fn (Builder $query) => $query->whereIn('type', ['cash_in', 'cash_out'])),
    ];
}

public function updatedActiveTab(): void
{
    $this->resetTable();
}

public function table(Table $table): Table
{
    
    if ($this->activeTab === 'transactions') {
        return $table
            ->columns([
                TextColumn::make('id')->label('#'),
                TextColumn::make('paymentMethod.name')
                    ->label(__('Payment Method'))
                    ->searchable(),
                TextColumn::make('description')
                    ->label(__('Description'))
                    ->limit(50)
                    ->searchable(),
                TextColumn::make('currency.code')
                    ->label(__('Currency'))
                    ->searchable(),
                TextColumn::make('type')
                    ->label(__('Operation'))
                    ->searchable()
                    ->badge(),
                TextColumn::make('amount')
                    ->label(__('Amount'))
                    ->formatStateUsing(function ($state) {
                        if ($state instanceof BigRational) {
                            $state = $state->toFloat();
                        } elseif (is_string($state) && str_contains($state, '/')) {
                            [$num, $den] = explode('/', $state);
                            if ($den != 0) {
                                $state = (float) $num / (float) $den;
                            }
                        }
                        $formatted = rtrim(rtrim(number_format($state, 8, '.', ''), '0'), '.');
                        return $formatted ?: '0';
                    }),
            ]);
    }
    
    
    return $table
    ->query(fn (Builder $query) => 
        $query->select([
            'payment_method_id',
            'type',
            'currency_id',
            \DB::raw('SUM(amount) as total_amount'),
        ])
        ->groupBy('payment_method_id', 'type', 'currency_id')
        ->with(['paymentMethod', 'currency']) // eager load para evitar N+1
    )
    ->columns([
        TextColumn::make('paymentMethod.name')
            ->label(__('Payment Method')),
        TextColumn::make('type')
            ->label(__('Type')),
        TextColumn::make('currency.code')
            ->label(__('Currency')),
        TextColumn::make('total_amount')
            ->label(__('Total Amount'))
            ->formatStateUsing(fn($state) => rtrim(rtrim(number_format((float) $state, 8, '.', ''), '0'), '.')),
    ]);

}

}

The namespaces in this file and the resource are correct. The "transactions" tab works perfectly. The error only appears when I switch to the "balances" tab, which uses a grouped/summed query.

I want to display grouped and summed transactions by currency, payment method, and type in the "balances" tab.