diff --git a/metadata/dbms/tools.js b/metadata/dbms/tools.js
index 40603d5..92f643b 100644
--- a/metadata/dbms/tools.js
+++ b/metadata/dbms/tools.js
@@ -1339,6 +1339,7 @@ class TWin
 
 	setCaption(val)
 	{
+		if(val==null) val='';
 		let obj=document.getElementById('TWin_Ca_'+this.tWinId);
 		if (typeof val === 'string' || val instanceof String)
 			obj.innerHTML=val;