WORLDSERVICE-336: Add conditional check (#12504)

Author: shayneahchoon

src/app/legacy/containers/ArticleMetadata/index.jsx

@@ -39,8 +39,12 @@ const ArticleMetadata = ({
         hasAmpPage={hasAmpPage}
       >
         <meta name="article:author" content={author} />
-        <meta name="article:modified_time" content={lastPublished} />
-        <meta name="article:published_time" content={firstPublished} />
+        {lastPublished && (
+          <meta name="article:modified_time" content={lastPublished} />
+        )}
+        {firstPublished && (
+          <meta name="article:published_time" content={firstPublished} />
+        )}
         {section && <meta name="article:section" content={section} />}
       </Metadata>
     )