Argument \"input\" has invalid value - input object GQL mutations

My tests were passing until I wrote the input_object block. In my ecto schema, the field title is non-null. Since I wanted the updation to take place with either title or slug(there are some cases when I don’t want to update the title but just the slug), I wrote the input_object. But this landed me in a new error which I am not able to fix. Invalid argument value.

Gql muation for update

@desc "Update a Post"
    field :update_post, :post do
      arg(:id, non_null(:string))
      arg(:title, :title_input)
      arg(:slug, :slug_input)
  
      resolve(&Resolvers.Post.update_post/3)
    end

input_object :title_input do
    field :title, :string
  end

  input_object :slug_input do
    field :slug, :string
  end

Resolver function

def update_post(_root, args, %{context: %{current_user: current_user}}) do
post_id = args.id
    post =
      Blog.get_post!(post_id)

    case Blog.update_post(
           post,
           args,
           current_user.current_tenant
         ) do
      {:ok, post} ->
        {:ok, post}

      {:error, changeset} ->
        {:error,
         message: "Could not update post",
         details: ChangesetErrors.error_details(changeset)}
    end

Mutation test

mutation = """
        mutation {
          updatePost(id: "#{context.post.id}", title: "New title") {
            id
            title
            slug
          }
        }
      """


      expected_response = %{
        "updatePost" => %{
          "id" => context.post.id,
          "title" => "New title"
        }
      }

Error message
"message" => "Argument \"title\" has invalid value \"New title\"."

Any help is appreciated.