Ruby on Rails

ActionView::Template::Error (undefined method `strftime' for nil:NilClass):

    28:         <%- locals = {:enewsletter => enewsletter} %>

    29:         <td nowrap="nowrap" class='enewsletter_name'><%= enewsletter.subscription.title %></td>

    30:                                       <td nowrap="nowrap"><%=enewsletter.title%></td>

    31:                                       <td nowrap="nowrap"><%=enewsletter.publication_date.strftime("%m/%Y")%></td>

    32:                                       <td nowrap="nowrap"> <%=enewsletter.require_ama_disclaimer%></td>

    33:                                       <td>

    34:                   <%#= link_to("Edit Release", edit_admin_release_path(release), edit_admin_release_path(release)) %> &nbsp;

  app/views/admin/enewsletters/index.html.erb:31:in `_app_views_admin_enewsletters_index_html_erb__1819630787_23456257799140_0'

  app/views/admin/enewsletters/index.html.erb:26:in `each'

  app/views/admin/enewsletters/index.html.erb:26:in `_app_views_admin_enewsletters_index_html_erb__1819630787_23456257799140_0'

  app/controllers/admin/enewsletters_controller.rb:17:in `index'

Please advise