<% avatar_url = if user.thumbnail.exists?
                  user.thumbnail(:medium)
                else
                  asset_path('staff/staff-default-avatar.png')
                end %>
<div class="staff">
  <%= link_to staff_path(user) do %>
    <div class="staff-pic" style="background-image: url('<%= avatar_url %>')"></div>
    <p class="text -author"><%= user.display_name %></p>
    <p class="text -meta"><%= user.current_position %></p>
  <% end %>
</div>

<% avatar_url = if user.thumbnail.file?
                  user.thumbnail(:medium)
                else
                  asset_path('staff/staff-default-avatar.png')
                end %>
<div class="staff">
  <%= link_to staff_path(user) do %>
    <div class="staff-pic" style="background-image: url('<%= avatar_url %>')"></div>
    <p class="text -author"><%= user.display_name %></p>
    <p class="text -meta"><%= user.current_position %></p>
  <% end %>
</div>

Use file instead of exists
Use file instead of exists
