Select element in a nested form

Hi everyone,

I am getting an error when i try to add a select in a nested form

The error no function clause matching in Keyword.pop/3

My select code:

<div class="field">
  <%= label f, :category, class: "label" %>
  <div class="control">

    <%= select f, :category_id, @categories, fn cf -> %>
    IO.inspect(@categories)
  </div>
  <p class="help is-danger"><%= error_tag cf, :category %></p>
  <% end %>
</div>

Update link to form as suggested by @benwilson512

https://github.com/wolfiton/blog_api/blob/master/lib/blog_api_web/templates/article/form.html.eex

Update error trace

[info] GET /articles/new
[]
[debug] Processing with BlogApiWeb.ArticleController.new/2
  Parameters: %{}
  Pipelines: [:browser]
[debug] QUERY OK source="categories" db=2.3ms
SELECT c0."id", c0."name", c0."slug", c0."inserted_at", c0."updated_at" FROM "categories" AS c0 []
[info] Sent 500 in 166ms
[error] #PID<0.840.0> running BlogApiWeb.Endpoint (connection #PID<0.839.0>, stream id 1) terminated
Server: localhost:4000 (http)
Request: GET /articles/new
** (exit) an exception was raised:
    ** (FunctionClauseError) no function clause matching in Keyword.pop/3
        (elixir) lib/keyword.ex:977: Keyword.pop(#Function<2.44023343/1 in BlogApiWeb.ArticleView."form.html"/1>, :value, nil)
        (phoenix_html) lib/phoenix_html/form.ex:1117: Phoenix.HTML.Form.selected/3
        (phoenix_html) lib/phoenix_html/form.ex:1099: Phoenix.HTML.Form.select/4
        (blog_api) lib/blog_api_web/templates/article/form.html.eex:29: anonymous fn/2 in BlogApiWeb.ArticleView."form.html"/1
        (phoenix_html) lib/phoenix_html/form.ex:377: Phoenix.HTML.Form.form_for/4
        (blog_api) lib/blog_api_web/templates/article/form.html.eex:1: BlogApiWeb.ArticleView."form.html"/1
        (blog_api) lib/blog_api_web/templates/article/new.html.eex:3: BlogApiWeb.ArticleView."new.html"/1
        (blog_api) lib/blog_api_web/templates/layout/app.html.eex:15: BlogApiWeb.LayoutView."app.html"/1
        (phoenix) lib/phoenix/view.ex:410: Phoenix.View.render_to_iodata/3
        (phoenix) lib/phoenix/controller.ex:729: Phoenix.Controller.__put_render__/5
        (phoenix) lib/phoenix/controller.ex:746: Phoenix.Controller.instrument_render_and_send/4
        (blog_api) lib/blog_api_web/controllers/article_controller.ex:1: BlogApiWeb.ArticleController.action/2
        (blog_api) lib/blog_api_web/controllers/article_controller.ex:1: BlogApiWeb.ArticleController.phoenix_controller_pipeline/2
        (phoenix) lib/phoenix/router.ex:288: Phoenix.Router.__call__/2
        (blog_api) lib/blog_api_web/endpoint.ex:1: BlogApiWeb.Endpoint.plug_builder_call/2
        (blog_api) lib/plug/debugger.ex:122: BlogApiWeb.Endpoint."call (overridable 3)"/2
        (blog_api) lib/blog_api_web/endpoint.ex:1: BlogApiWeb.Endpoint.call/2
        (phoenix) lib/phoenix/endpoint/cowboy2_handler.ex:42: Phoenix.Endpoint.Cowboy2Handler.init/4
        (cowboy) /home/dan/Codes/blog_api/deps/cowboy/src/cowboy_handler.erl:41: :cowboy_handler.execute/2
        (cowboy) /home/dan/Codes/blog_api/deps/cowboy/src/cowboy_stream_h.erl:320: :cowboy_stream_h.execute/3

Update article controller
https://github.com/wolfiton/blog_api/blob/master/lib/blog_api_web/controllers/article_controller.ex
Update migrations for articles and categories
https://github.com/wolfiton/blog_api/blob/master/priv/repo/migrations/20191203154052_create_articles.exs
https://github.com/wolfiton/blog_api/blob/master/priv/repo/migrations/20191213160415_create_categories.exs

Schemas and contexts

https://github.com/wolfiton/blog_api/blob/master/lib/blog_api/blog/article.ex

https://github.com/wolfiton/blog_api/blob/master/lib/blog_api/categories/category.ex

https://github.com/wolfiton/blog_api/blob/master/lib/blog_api/blog.ex

https://github.com/wolfiton/blog_api/blob/master/lib/blog_api/categories.ex

Also if there are any suggestions for the rest of my code the full code here https://github.com/wolfiton/blog_api
Thanks in advance