BAPI_MATERIAL_BOM_GROUP_CREATE cannot set "Fixed Qty" = "" (Item cat.'T')

Hi All,

I got the problem that BAPI_MATERIAL_BOM_GROUP_CREATE cannot set "Fixed Qty" = "" when item category = "T". It always set = 'X', after finish BOM creation. Is it about the default value somewhere in this BAPI? How can I fix this?

Thank you very much