fix: Update overview.html.eex (#11094)

apps/block_scout_web/lib/block_scout_web/templates/block/overview.html.eex

@@ -161,15 +161,17 @@
             <dd class="col-sm-9 col-lg-10"><%= @block.difficulty |> Decimal.to_integer() |> BlockScoutWeb.Cldr.Number.to_string! %></dd>
           </dl>
           <%= if block_type(@block) == "Block" do %>
-            <!-- Total Difficulty -->
-            <dl class="row">
-              <dt class="col-sm-3 col-lg-2 text-muted">
-                <%= render BlockScoutWeb.CommonComponentsView, "_i_tooltip_2.html",
-                text: gettext("Total difficulty of the chain until this block.") %>
-                <%= gettext("Total Difficulty") %>
-              </dt>
-              <dd class="col-sm-9 col-lg-10"><%= @block.total_difficulty |> Decimal.to_integer() |> BlockScoutWeb.Cldr.Number.to_string! %></dd>
-            </dl>
+            <%= if !is_nil(@block.total_difficulty) do %>
+              <!-- Total Difficulty -->
+              <dl class="row">
+                <dt class="col-sm-3 col-lg-2 text-muted">
+                  <%= render BlockScoutWeb.CommonComponentsView, "_i_tooltip_2.html",
+                  text: gettext("Total difficulty of the chain until this block.") %>
+                  <%= gettext("Total Difficulty") %>
+                </dt>
+                <dd class="col-sm-9 col-lg-10"><%= @block.total_difficulty |> Decimal.to_integer() |> BlockScoutWeb.Cldr.Number.to_string! %></dd>
+              </dl>
+            <% end %>
             <!-- Gas Used -->
             <dl class="row">
               <dt class="col-sm-3 col-lg-2 text-muted">