Show headers in mailer previews only if there are headers present

Author: guilleiguaran

railties/lib/rails/templates/rails/mailers/email.html.erb

@@ -125,21 +125,23 @@
         </select>
       </dd>
     <% end %>
-    
-    <dt>Headers:</dt>
-    <dd>
-      <details>
-        <summary>Show all headers</summary>
-        <table>
-        <% @email.header_fields.each do |field| %>
-          <tr>
-            <td align="right" style="color: #7f7f7f"><%= field.name %>:</td>
-            <td><%= field.value %></td>
-          </tr>
-        <% end %>
-        </table>
-      </details>
-    </dd>
+
+    <% unless @email.header_fields.nil? || @email.header_fields.empty? %>
+      <dt>Headers:</dt>
+      <dd>
+        <details>
+          <summary>Show all headers</summary>
+          <table>
+          <% @email.header_fields.each do |field| %>
+            <tr>
+              <td align="right" style="color: #7f7f7f"><%= field.name %>:</td>
+              <td><%= field.value %></td>
+            </tr>
+          <% end %>
+          </table>
+        </details>
+      </dd>
+    <% end %>
 
     <dt>EML File:</dt>
     <dd><%= link_to "Download", action: :download %></dd>