current_userを存在するようにしたい

前提・実現したいこと

@current_userが存在している状態にしたい。

発生している問題・エラーメッセージ

projects_controller.rbの8行目、user_id：　@current_user.idに対し、

NoMethodError in ProjectsController#create

undefined method `id' for nil:NilClass

該当のソースコード

application_controller.rb

class ApplicationController < ActionController::Base
  before_action :set_current_user

  def set_current_user
    @current_user = User.find_by(id: session[:user_id])
  end

projects_controller.rb

def create
    @project = Project.new(
      title: params[:title],
      contents: params[:contents],
      wanted: params[:wanted],
      contact_info: params[:contact_info],
      comments: params[:comments],
      user_id: @current_user.id
    )

    if @project.save
      flash[:notice] = "プロジェクトを作成しました"
      redirect_to("/projects/index")
    else
      render("projects/new")
    end
  end

users_controller.rb

def create
    @user = User.new(
      email: params[:email],
      password: params[:password]
    )

    if @user.save
      session[:user_id] = @user.id
      flash[:notice] = "ユーザー登録が完了しました"
      redirect_to("/users/profile/#{@user.id}")
    else
      render("signup")
    end
  end
end

ログ

Started POST "/projects/create" for ::1 at 2019-06-30 20:31:15 +0900
  ActiveRecord::SchemaMigration Load (0.2ms)  SELECT "schema_migrations".* FROM "schema_migrations"
/Users/kyohei/Desktop/match/match_app/app/controllers/application_controller.rb:9: warning: found = in conditional, should be ==
Processing by ProjectsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"Lcc2pEJVb00UAjmTnTTTJuBrIOh5xoP4EFVkQMoWAnXmHRHJ3D5ICF3KfjCox8yh0NzstWnf2ueGxG29QH4WiA==", "title"=>"s", "contents"=>"s", "wanted"=>"", "contact_info"=>"s", "comments"=>""}
  User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 5], ["LIMIT", 1]]
Completed 500 Internal Server Error in 18ms (ActiveRecord: 0.6ms)



NoMethodError (undefined method `id' for nil:NilClass):

app/controllers/projects_controller.rb:23:in `create'
  Rendering /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout
  Rendering /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/_source.html.erb
  Rendered /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/_source.html.erb (1.9ms)
  Rendering /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb
  Rendered /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (1.1ms)
  Rendering /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb
  Rendered /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (1.1ms)
  Rendered /Users/kyohei/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/actionpack-5.0.7.2/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout (72.8ms)
^C- Gracefully stopping, waiting for requests to finish
=== puma shutdown: 2019-06-30 20:59:10 +0900 ===

試したこと

session[:user_id]も正しく数値が入れられており、DBのusersテーブルにもユーザーは存在しています。しかし@current_userが存在しないとなってしまうのはなぜでしょうか。