I keep running into the following error "undefined method `user' for nil:NilClass"

Everything was working fine but I added stuff to my original scaffold, Specifically this line of code. "rails g migration add_first_name_and_last_name_to_users first_name:string last_name:string bio:text" After this I did "rake db:migrate" and added the fields. After working out the error I can't get past this new one.

Here is my users_controller.rb,

class UsersController < ApplicationController
  before_action :set_user, only: [:show, :edit, :update, :destroy]
  after_action :signed_in_after_register, only: :create 

  def index
    @users = User.all
    @user = User.find(session[:user_id])
  end

  def dashboard 
    @user = User.find(session[:user_id]) unless session[:user_id] == ""
    redirect_to login_path, notice: "You're not logged in" unless @user 
    @posts = @user.posts.order("created_at DESC").limit(3)
  end 

  def newsfeed
    @user = User.find(session[:user_id]) unless session[:user_id] == nil
    redirect_to login_path, notice: "You're not logged in" unless @user 
  end

  def nav
    @user = User.find(session[:user_id])
  end

  def destroy
    @user = User.find(session[:user_id])
  end

  def welcome
    @user = User.find(session[:user_id])
  end

  def show
    @user = User.find(session[:user_id]) unless session[:user_id] == ""
    redirect_to login_path, notice: "You're not logged in" unless @user 
    @posts = @user.posts.order("created_at DESC").limit(3)
  end

  def new
    @post = Post.new(params[:post_id])
    @user = User.new
  end

  def edit

  end

  def create
    @post.user = @current.user
    @user = User.new(user_params)

    respond_to do |format|
      if @user.save
        format.html { redirect_to profile_path, notice: 'User was successfully created.' }
        format.json { render :show, status: :created, location: @user }
      else
        format.html { render :new }
        format.json { render json: @user.errors, status: :unprocessable_entity }
      end
    end
  end

  def update
    respond_to do |format|
  if @user.update(user_params)
    format.html { redirect_to dashboard_path, notice: 'User was successfully updated.' }
    format.json { render :show, status: :ok, location: @user }
      else
    format.html { render :edit }
    format.json { render json: @user.errors, status: :unprocessable_entity }
          end
        end
      end

  def destroy
    @user.destroy
    respond_to do |format|
      format.html { redirect_to users_url, notice: 'User was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    def set_user
      @user = User.find(params[:id])
    end
    def signed_in_after_register 
      session[:user_id] = @user.id 
    end

    def user_params
      params.require(:user).permit(:first_name, :last_name, :bio, :name, :password, :password_confirmation, :email, :age, :profile_picture, :post)
    end
end

This is in my _form.html.erb

<%= form_for @user, html: { multipart: true } do |f| %>
  <% if @user.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@user.errors.count, "error") %> prohibited this user from being saved:</h2>

      <ul>
      <% @user.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>
<div class="sign_up_form_2">
  <div class="field">
    <%= f.label :first_name %>
    <%= f.text_field :first_name, placeholder: "First Name", class: "form-control" %>
  </div>
  <div class="field">
    <%= f.label :last_name %>
    <%= f.text_field :last_name, placeholder: "Last Name", class: "form-control" %>
  </div>
  <div class="field">
    <%= f.label :User_name %><br>
    <%= f.text_field :name, placeholder: "User Name", class: "form-control" %>
  </div>
  <div class="field">
    <%= f.label :email %><br>
    <%= f.text_field :email, placeholder: "Email", class: "form-control" %>
  </div>
  <div class="field">
    <%= f.label :age %><br>
    <%= f.number_field :age, placeholder: "Age", class: "form-control" %>
  </div>
  <div class="field">
    <%= f.label :password %><br>
    <%= f.password_field :password, placeholder: "Password", class: "form-control" %>
  </div>
  <div class="field">
    <%= f.label :password_confirmation %><br>
    <%= f.password_field :password_confirmation, placeholder: "Password Confirmation", class: "form-control" %>
  </div><br>
  <div class="field">
    <%= f.label :profile_picture %>
    <%= f.file_field :profile_picture %><br>
  </div>
  <div class="actions">
    <%= f.submit "Create Account", class: "btn btn-default btn-sign-up" %>
  </div>

    <% end %>
</div>

If there is any other code you need to see to get a better understand then please let me know! I've been stuck on this for an hour now and I'm sure its pretty simple, Thanks in advance!