Quick fix on target cpa with amount null

Author: timothymarois

src/Services/GoogleAds/Operations/Campaign.php

@@ -175,6 +175,8 @@ public function getTargetCpa()
         {
             $strategy =@ $this->response()->getBiddingStrategyConfiguration()->getBiddingScheme() ?? null;
 
+            $amount = null;
+            
             if ($strategy) {
                 $tcpa =@ $strategy->getTargetCpa();
                 if ($tcpa) {