Thumbs: guard against derivatives that don't exist yet

Addresses: geobtaa/geoblacklight_admin#55

Gemfile

@@ -82,7 +82,7 @@ gem 'twitter-typeahead-rails', '0.11.1.pre.corejavascript'
 gem 'geoblacklight', '4.4'
 
 # GBL Admin
-gem 'geoblacklight_admin', git: "https://github.com/geobtaa/geoblacklight_admin.git", branch: "develop"
+gem 'geoblacklight_admin', git: "https://github.com/geobtaa/geoblacklight_admin.git", branch: "guard-nil-derivative"
 gem 'git', ">= 1.13"
 gem "rubyzip", ">= 1.3.0"
 gem "awesome_print"

Gemfile.lock

@@ -41,8 +41,8 @@ GIT
 
 GIT
   remote: https://github.com/geobtaa/geoblacklight_admin.git
-  revision: a2e7919b04d63b3ab45195f26b9dec62bfbfdc24
-  branch: develop
+  revision: dc3776c11e0e269e735c0633f340839472aaadc2
+  branch: guard-nil-derivative
   specs:
     geoblacklight_admin (0.4.1)
       active_storage_validations (~> 1.0)

app/views/catalog/_index_mapview_default.html.erb

@@ -42,7 +42,15 @@
               <td style="text-align: center;">AWS S3</td>
             </tr>
             <tr>
-              <td><%= image_tag document.model.thumbnail.file_url(:thumb_standard_2X) %></td>
+              <td>
+                <% if document&.model&.thumbnail&.file_url(:thumb_standard_2X).nil? %>
+                  <span class="icon square mr-3">
+                    <%= geoblacklight_icon(document[Settings.FIELDS.RESOURCE_CLASS]&.first, classes: 'svg_tooltip') %>
+                  </span>
+                <% else %>
+                  <%= image_tag document&.model&.thumbnail&.file_url(:thumb_standard_2X) %>
+                <% end %>
+              </td>
             </tr>
           </table>
         <% end %>