Fix segmentation fault in nr-ru

executables/nr-ru.c

@@ -746,7 +746,7 @@ void tx_rf(RU_t *ru,int frame,int slot, uint64_t timestamp) {
       // currently we switch beams every 10 slots (should = 1 TDD period in FR2) and we take the beam index of the first symbol of the first slot of this period
       int beam=0;
       if (slot%10==0) {
-	if (ru->common.beam_id[0][slot*fp->symbols_per_slot] < 8) {
+        if ( ru->common.beam_id && (ru->common.beam_id[0][slot*fp->symbols_per_slot] < 8)) {
           beam = ru->common.beam_id[0][slot*fp->symbols_per_slot] | 8;
         }
       }