rails フォロー機能を作ったらエラーが出る

Question

https://qiita.com/MitsuguSueyoshi/items/e41e2ff37f143db81897のサイトをもとにフォロー機能を作っていたのですがエラーが出てしまいます。qiitaのコメント欄にも似たようなエラーになったという方がいて解決方法？のようなことが書かれていましたが試しても動きませんでした。解決方がわかる方は、回答・コメントお願いします。

Started POST "/relationships" for ::1 at 2020-03-14 17:19:53 +0900
Processing by RelationshipsController#create as HTML
  Parameters: {"authenticity_token"=>"Sf3vgfyTOP3JKBT9ZzShGA0PqzBAXDhh8mH6m1jIMGXG7RlYrYZ0QhScuj0fNjIWKK5b/jdqJ/JMzQjj9ZQy+w==", "follow_id"=>"2", "commit"=>"Follow"}
Completed 500 Internal Server Error in 5ms (ActiveRecord: 0.0ms | Allocations: 1189)



NoMethodError (undefined method `[]' for nil:NilClass):

app/controllers/relationships_controller.rb:19:in `set_user'

class RelationshipsController < ApplicationController
    before_action :set_user

    def create
      man = Man.find(params[:relationship][:follow_id])
      following = current_man.follow(man)
      redirect_to "questions"
    end
  
    def destroy
      man = Man.find(params[:relationship][:follow_id])
      following = current_man.unfollow(man)
      redirect_to "questions"
    end
  
    private
  
    def set_user
      man = Man.find(params[:relationship][:follow_id])
    end

end

    <%= form_for(current_man.relationships.build) do |f| %>
      <%= hidden_field_tag :follow_id, man.id %>
      <%= f.submit 'Follow' %>
    <% end %>

class Man < ApplicationRecord
  has_many :relationships
  has_many :followings, through: :relationships, source: :follow
  has_many :reverse_of_relationships, class_name: 'Relationship', foreign_key: 'follow_id'
  has_many :followers, through: :reverse_of_relationships, source: :man

  def follow(other_man)
    unless self == other_man
     self.relationships.find_or_create_by(follow_id: other_man.id)
    end
  end
  
  def unfollow(other_man)
    relationship = self.relationships.find_by(follow_id: other_man.id)
    relationship.destroy if relationship
  end
  
  def following?(other_man)
    self.followings.include?(other_man)
  end
end

class Relationship < ApplicationRecord
    belongs_to :man
    belongs_to :follow, class_name: 'Man'
  
    validates :man_id, presence: true
    validates :follow_id, presence: true
end

Answer 1

Parameters　をみると
{"authenticity_token"=>"。。", "follow_id"=>"2", "commit"=>"Follow"}
となっています。
ですので
params[:relationship][:follow_id]　は　nil[:follow_id] となります。
params[:follow_id]　
とするか、もしくは
hidden_field_tag :follow_id, man.id　を
f.hidden_field :follow_id, man.id にしてください