Index: src/wp-includes/general-template.php
===================================================================
--- src/wp-includes/general-template.php	(revision 33603)
+++ src/wp-includes/general-template.php	(working copy)
@@ -746,7 +746,9 @@
 			$size_data = array( $size, $size );
 		}
 		$url_data = wp_get_attachment_image_src( $site_icon_id, $size_data );
-		$url = $url_data[0];
+		if ( $url_data ) {
+			$url = $url_data[0];
+		}
 	}
 
 	return $url;
@@ -770,7 +772,7 @@
  * @return bool
  */
 function has_site_icon( $blog_id = null ) {
-	return !! get_site_icon_url( $blog_id, 512 );
+	return (bool) get_site_icon_url( $blog_id, 512 );
 }
 
 /**