Issue #3511960: Fix type error when size is null in formatter.

Closes #3511960

src/Plugin/Field/FieldFormatter/FileLinkSeparateFormatter.php

@@ -30,10 +30,8 @@ class FileLinkSeparateFormatter extends LinkSeparateFormatter {
     foreach ($items as $delta => $item) {
       if (isset($element[$delta])) {
         $element[$delta]['#theme'] = 'file_link_formatter_link_separate';
-        $element[$delta] += [
-          '#size' => $this->getSetting('format_size') ? ByteSizeMarkup::create($item->size) : $item->size,
-          '#format' => $item->format,
-        ];
+        $element[$delta]['#size'] = $this->getSetting('format_size') ? ByteSizeMarkup::create($item->size ?? 0) : $item->size;
+        $element[$delta]['#format'] = $item->format;
       }
     }
     return $element;