No function clause matching in Ecto.Changeset.cast

Hey all! New to Elixir - I’m trying to edit an entry in postgresql, and I can’t see what I’m doing wrong - I keep getting this error when I try to access the URL. Want to be seeing a page with the entry passed in by its “id” in the path. see below:

router.ex:

 scope "/", Discuss do
    pipe_through :browser 

    get "/", TopicController, :index
    get "/topics/new", TopicController, :new
    post "/topics", TopicController, :create
    get "/topics/:id/edit", TopicController, :edit
    put "/topics/:id", TopicController, :update
  end

controller:

  def edit(conn, %{"id" => topic_id}) do
    topic = Repo.get(Topic, topic_id)
    changeset = Topic.changeset(topic)

    render conn, "edit.html", changeset: changeset, topic: topic
  end

model:

defmodule Discuss.Topic do
  use Discuss.Web, :model

  schema "topics" do
    field :title, :string
  end

  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [:title])
    |> validate_required([:title])
  end

I think I may have done something wrong in the controller edit function, but for the life of me I can’t figure out what. Any help appreciated. Thanks!

41%20PM2350×1798 263 KB

In any case, if someone could make the error here a little less ambiguous, I’m sure that would help to. Thanks!