Various code cleanup

app/Http/Controllers/Chart/ExpenseReportController.php

@@ -185,6 +185,7 @@ class ExpenseReportController extends Controller
         // remove all empty entries to prevent cluttering:
         $newSet = [];
         foreach ($chartData as $key => $entry) {
+            // TODO not sure, this is a bad comparison.
             if (0 === !array_sum($entry['entries'])) {
                 $newSet[$key] = $entry;
             }

app/Http/Controllers/Chart/PiggyBankController.php

@@ -83,7 +83,7 @@ class PiggyBankController extends Controller
         // get first event or start date of piggy bank or today
         $startDate = $piggyBank->startdate ?? today(config('app.timezone'));
 
-        /** @var PiggyBankEvent $firstEvent */
+        /** @var PiggyBankEvent|null $firstEvent */
         $firstEvent = $set->first();
         $firstDate  = null === $firstEvent ? new Carbon() : $firstEvent->date;