problem of nested <filter> tag in XML categories file

[yukio.kurihara-a@xxxxxxxxxxxxxxxx]

hello
 I need your help.

 I am trying to sort variables and created XML categories file.
 my problem is that nested XML tag <filter> causes abnormal termination of
 the genLAS.pl with the error message as follows:

 Internal: Unknown type/class combo:
 variable/LAS::Category::Filter::Dataset at ../xml/perl/LASServlet.pm line
 2429.


 the XML code, I extracted from the LAS online manual,  is

 <category name="Sea Currents">
   <filter action="apply-dataset" contains="JMA">
     <filter action="apply-variable" contains="current"/>
   </filter>
 </category>


 on the other hand, the following code works well.

 <category name="Sea Currents">
   <filter action="apply-variable" contains="current"/>
 </category>


 my LAS is 6.2.0


 thank you.


 Yukio Kurihara
 Office of marine prediction, JMA
 e-mail : yukio.kurihara-a@met.kishou.go.jp