views_aggregator-3485063: If field is not found, an error is thrown on views with relationships

Closes #3485063

src/Plugin/views/style/Table.php

@@ -1120,7 +1120,7 @@ class Table extends ViewsTable {
       }
     }
     // Value not found - mark the field and exit.
-    else {
+    if (empty($field)) {
       return 'Not found: ' . $field_name . ' > ' . $raw_value;
     }