Cannot update a column value to null?

I have a foreign key column in my table, call it parentId, when parentId is null, i know that the current row has no parent. If it is not null then I can use that foreign key to connect with the corresponding parent. When trying to use update in prisma, i run into a few issues:

First, I cannot directly update the value of parentId or any foreign key for that matter, and instead an error is thrown and I am basically told that parentId field doesnt exist and instead what im looking for is the relation field parent. So the below does not work

db.folder.update({
    data: {
      parentId: obj.id
    },
    where: { id },
  })

So when i try to instead update the relation field parent like this:

db.folder.update({
    data: {
      parent:
         {
              connect: {
                id: obj.id,
              },
            },
    },
    where: { id },
  })

Then if obj.id is null, an error is thrown because you cant connect with a null id, so instead i add a conditional,

db.folder.update({
    data: {
      parent:
        obj.id == null
          ? null
          : {
              connect: {
                id: obj.id,
              },
            },
    },
    where: { id },
  })

And this does not work either, instead every time i pass in null, the value in the db is not changed, which i guess is a safeguard so that if no parameter is passed in, it doesnt nullify the value. However, I need to update the value of parentId to be null in certain cases… How can i do that??