How to solve error (undefined method `name' for nil:NilClass)

I am getting this error , how to solve this relation error

i have a model called property.rb

class Property < ActiveRecord::Base
    belongs_to :rm
    belongs_to :category
end

also i have category.rb

class Category < ActiveRecord::Base
    has_many :rms,dependent: :destroy
    has_many :properties,dependent: :destroy
end

my RM(relationship Manager) model is

class Rm < ActiveRecord::Base
  acts_as :user
  belongs_to :category
  has_many :properties
end

in my controller i listing properties like this

class Rms::PropertiesController < ApplicationController
  before_filter :authenticate_user!
  before_action :set_property, only: [:show, :edit, :update, :destroy]
  def index
    @properties = Property.all
  end
 def property_params
 params.require(:property).permit(:seller_name,:rm_id,:category_id,:property_type_id,:seller_email,:seller_phone,:property_name)
  end
end

in my view page i am listing the property added by RM in index.html.erb

    <% @properties.each do |property| %>
      <tr>
        <td><%= property.seller_name %></td>
        <td><%= property.seller_email %></td>
        <td><%= property.seller_phone %></td>
        <td><%= property.category.name %></td>
        <td><%= property.property_name %></td>
   <% end %>