NestJS/TypeORM error: The value passed as UUID is not a string when inserting record - postgresql

Question

I created a NestJS sample application that uses TypeORM to access the Postgres database.
The complete codes can be found from this link.
There are two entities like this.
#Entity({ name: 'posts' })
export class PostEntity {
#PrimaryGeneratedColumn('uuid')
id?: string;
#Column()
title: string;
#Column({ nullable: true })
content?: string;
#OneToMany((type) => CommentEntity, (comment) => comment.post, {
cascade: true,
})
comments?: Promise<CommentEntity[]>;
#ManyToOne((type) => UserEntity, { nullable: true })
#JoinColumn({ name: 'author_id' })
author?: UserEntity;
#RelationId((post: PostEntity) => post.author)
authorId?: string;
#CreateDateColumn({ name: 'created_at', type: 'timestamp', nullable: true })
createdAt?: Date;
#UpdateDateColumn({ name: 'updated_at', type: 'timestamp', nullable: true })
updatedAt?: Date;
}
#Entity({ name: 'comments' })
export class CommentEntity {
#PrimaryGeneratedColumn('uuid')
id: string;
#Column()
content: string;
#ManyToOne((type) => PostEntity, (p) => p.comments)
#JoinColumn({ name: 'post_id' })
post: PostEntity;
#RelationId((comment: CommentEntity) => comment.post)
postId?: string;
#CreateDateColumn({ name: 'created_at', type: 'timestamp' })
createdAt: Date;
}
When adding a comment through the GraphQL endpoint, which will call the following codes.
addComment(id: string, comment: string): Observable<Comment> {
const entity = new CommentEntity();
Object.assign(entity, {
content: comment,
postId: id,
});
return from(this.commentRepository.save(entity)).pipe(
map((c) => {
return { id: c.id, content: c.content } as Comment;
}),
);
}
When running the e2e tests it will fail due to an error message(I added a console.log to print the GraphQL errors in the response body):
addComment errors: [{"message":"The value passed as UUID is not a string"}]