first argument in form cannot contain nil or be empty in edit on ruby on rails

i just cant figured out what kind of error i get. i stuck in editing. So here's my code

posts_controller.rb

class PostsController < ApplicationController
def index
    @posts = Post.all
end

def show
    @post = Post.find(params[:id])
end

def new
    @post = Post.new
end

def create
    @post = Post.new(user_params)
    #   @post = Post.new(params[:post])

    if @post.save
        redirect_to posts_path, :notice => "Your post was saved"
    else
        render "new"
    end
end

private

def user_params
    params.require(:post).permit(:title, :content)
end

def edit
    @post = Post.find(params[:id])
end

def update

end

def destroy

end

end

And here's my edit.html.erb

<h1>Edit Post</h1>

<%= form_for @post do |f| %>
   <p>
      <%= f.label :title %>
   </p>
<% end %>

And the error i got is "First argument in form cannot contain nil or be empty"