Rails/Comment function: undefined method `comment' for nil:NilClass

i want to create a function for comments for my rails application. Therefore only the current_user or an admin (i use active_admin) should be able to delete his comment. But i have trouble to figure that one out because my methods seem to point to nil. can someone help me out please?

My comments_controller.rb

class CommentsController < ApplicationController

before_action :correct_user,   only: :destroy


def create 
    @post =Post.find(params[:post_id])
    @comment =@post.comments.create(params[:comment].permit(:name, :body))
    redirect_to post_path(@post)
end


def destroy 
    @post = Post.find(params[:post_id])
    @comment= @post.comments.find(params[:id])
    @comment.destroy
    redirect_to post_path(@post)
end

private

def correct_user
  @user= User.find(current_user.id)
  redirect_to(root_url) unless current_user.id == @post.comment.user.id
end

end

In my correct_user method the undefined comment shows up, so i already tried to add

@post = Post.find(params[:post_id])    
@comment= @post.comments.find(params[:id])

and tried different ways to make this run.

my comment.rb

 class Comment < ApplicationRecord
 belongs_to :post
 end

my post.rb

class Post < ApplicationRecord
  belongs_to :user
  has_many :comments, dependent: :destroy

  validates :title, presence: true, length: {minimum: 5}
  validates :body, presence: true
  validates :user, presence: true
  validates :user_id, presence: true
  has_attached_file :image  #, :styles => { :medium => "300x300>", :thumb => 
  "100x100>" }
  validates_attachment_content_type :image, :content_type => /\Aimage\/.*\Z/
end

and my user.rb

class User < ApplicationRecord
 has_many :posts

 devise :database_authenticatable, :registerable,
     :recoverable, :rememberable, :trackable, :validatable  
end

Can someone help me?

PS: i want to do this rather with an before action, then with an if-statement around the delete link.