try/catch - not catched

hi,

when I try this :

var = ''
try
    var->$objecttype() 
catch e
   print 'error ':e->$tojson() 
endtry 
print 'finished'

the error is not cached, the program terminate with echo bad self type: 2 and @SYSTEM.RETURN.CODE = -1 

Same behavior with the $fromjson(), $tojson() ... 

any idea ?