EMPIREDB-394 another small fix
diff --git a/empire-db/src/main/java/org/apache/empire/db/DBSQLBuilder.java b/empire-db/src/main/java/org/apache/empire/db/DBSQLBuilder.java
index d9a088a..f84ed40 100644
--- a/empire-db/src/main/java/org/apache/empire/db/DBSQLBuilder.java
+++ b/empire-db/src/main/java/org/apache/empire/db/DBSQLBuilder.java
@@ -287,7 +287,7 @@
         }
         if (ObjectUtils.isEmpty(value))
         {   // null
-            sql.append(DBSqlPhrase.SQL_NULL);
+            append(DBSqlPhrase.SQL_NULL);
             return;
         }
         // set string buffer