Hello Sheelam,
When creating a shopping cart, default product category will be proposed, even if no default category is defined in PPOMA_BBP. In such case, system will take the first product category found and display it to the user.
In standard, it is no possible to have a blank product category in shopping cart.
Having said that, there is a consulting note 1498455 available, which is relevant for cases when you add an item to shopping cart via pop-up window, using add item button (shopping card wizard/free text item). If this note is applied, blank product category will be displayed in the pop-up.
However, if you are creating a new shopping cart using the professional screen, you will be able to see the default product category.
You could also adopt a workaround that is being used by many other customers.
As a workaround they create a "dummy" product category with description like "select product category" and set this one as default.
Then if the user tries to use this product category, error message is raised saying to select a different product category (via BBP_DOC_CHECK_BADI). Then end user would be forced to select a different one.
I hope the above information helps.
Best Regards,
Monalisa