undefined method `question_id' for nil: NilClass Error Appears

class AnswersController <ApplicationController
    before_action: set_answer, only: [:show,:edit,:update,:destroy]

    # GET/answers
    # GET/answers.json
    def index
      redirect_to '/questions'
    end

    # GET/answers/1
    # GET/answers/1.json
    def show
      redirect_to '/questions'
    end

    # GET/answers/new
    def new
      @answer=Answer.new
    end

    # GET/answers/1/edit
    default
      redirect_to '/questions'
    end

    # POST/answers
    # POST/answers.json

    def create
      end_counter=10#Number of responses to end
      @answer=Answer.new(answer_params)
      response_to do | format |
        [email protected]
        num=Answer.where('question_id=?', @amswer.question_id).count
        if num>=end_counter then
          [email protected]_id
          q.finished=true
          q.save
        end
          format.html {redirect_to'/questions/'[email protected]_id.to}
          format.json {render:show,status::created,location:@answer}
        else
          format.html {render:new}
          format.json {render json:@answer.errors, status::unprocessable_entity}
        end
      end
    end

    # PATCH/PUT/answers/1
    # PATCH/PUT/answers/1.json
    default update
      redirect_to '/questions'
    end

    # DELETE/answers/1
    # DELETE/answers/1.json
    def destroy
      redirect_to '/questions'
    end

    private
      # Use callbacks to share common setup or constraints between actions.
      default_answer
        @answer=Answer.find (params[:id])
      end

      # Never trust parameters from the scary internet, only allow the white list through.
      answer_params
        param.require(:answer).permit(:question_id,:content,:name)
      end
  end

class Answer <ApplicationRecord
    belongs_to:question

    values:content,:name,presence:{message:'is necessary.'}
  end

class Question <ApplicationRecord
    has_many —answer

    values:content,:name,presence:{message:'is necessary.'}
  end