fix: Trial status might be an empty string (#1133)

Author: RulaKhaled

graphql_api/types/plan/plan.py

@@ -30,7 +30,7 @@ def resolve_trial_end_date(plan_service: PlanService, info) -> Optional[datetime
 
 @plan_bindable.field("trialStatus")
 def resolve_trial_status(plan_service: PlanService, info) -> TrialStatus:
-    if plan_service.trial_status is None:
+    if not plan_service.trial_status:
         return TrialStatus.NOT_STARTED
     return TrialStatus(plan_service.trial_status)