Hi Abdullah,
FPM is not defaulting an empty line.
In my model the relationship HAS_COMP is the leading relationship and the relationship QLF_COMP is the qualifying relationship. This creates a BP_HEADER + ZCOMPR_ID key, isn't it?
We have redefined the IF_FPM_GUIBB_LIST~GET_DATA method and after calling the superclass method we add our custom code. After that, the CT_DATA global variable is filled correctly, and without a duplicate key (BP_HEADER + ZCOMPR_ID).