FPM - create_empty_rows not creating default key

Hi Experts,

Need your help , i used the below code to create a new

                lr_s_amnppe_item ?= lo_ctrl_node->create_empty_row( abap_true ).  but it not retirning Key in structure   lr_s_amnppe_item.

wheni debug the check statement       CHECK ms_node_config-node_class IS NOT INITIAL is getting failed. Can you please help in knowing the process behind ms_node_config-node_class to be filled. thank you