PLATFORM-10342| avoid deprecation messages when calling getMsgFromNamespace()

Author: harnash

includes/language/MessageCache.php

@@ -1352,7 +1352,7 @@ public function getMsgFromNamespace( $title, $code ) {
 			$entry = $this->loadCachedMessagePageEntry(
 				$title,
 				$code,
-				$this->cache->getField( $code, 'HASH' )
+				$this->cache->getField( $code, 'HASH' ) || ''
 			);
 		} else {
 			// Message page either does not exist or does not override a software message
@@ -1363,7 +1363,7 @@ public function getMsgFromNamespace( $title, $code ) {
 				$entry = $this->loadCachedMessagePageEntry(
 					$title,
 					$code,
-					$this->cache->getField( $code, 'HASH' )
+					$this->cache->getField( $code, 'HASH' ) || ''
 				);
 			}
 			if ( $entry === null || substr( $entry, 0, 1 ) !== ' ' ) {