How we can prevent null value in a nullable input field?

[huyhqvmogroup]

@InputType()
export class UpdateUserInput {
  @Field({ nullable: true})
  name: string
  
  @Field({ nullable: true })
  @IsNotNull() // a custom validation
  isDeleted?: bolean
}

I just want to update exactly the fields the user submits, but the nullable option allows null values and they can be unexpectedly updated to null in my database.
In some cases, I may also want to update fields to null as a way to unset such fields
We can use custom validation but it seems to be ignored by nullable option
What should I do? or something wrong in my mindset?