[backend] Fix null for objectParticipant in Task (#9752)

Co-authored-by: BocognanoSarah <sarah.bocognano@filigran.io>

opencti-platform/opencti-graphql/src/modules/task/task-resolvers.ts

@@ -1,5 +1,7 @@
 import type { Resolvers } from '../../generated/graphql';
 import { findAll, findById, taskAdd, taskAddRelation, taskContainsStixObjectOrStixRelationship, taskDelete, taskDeleteRelation, taskEdit } from './task-domain';
+import { loadThroughDenormalized } from '../../resolvers/stix';
+import { INPUT_PARTICIPANT } from '../../schema/general';
 
 const taskResolvers: Resolvers = {
   Query: {
@@ -9,6 +11,9 @@ const taskResolvers: Resolvers = {
       return taskContainsStixObjectOrStixRelationship(context, context.user, args.id, args.stixObjectOrStixRelationshipId);
     },
   },
+  Task: {
+    objectParticipant: (container, _, context) => loadThroughDenormalized(context, context.user, container, INPUT_PARTICIPANT, { sortBy: 'user_email' }),
+  },
   Mutation: {
     taskAdd: (_, { input }, context) => taskAdd(context, context.user, input),
     taskDelete: (_, { id }, context) => taskDelete(context, context.user, id),