Add some null pointer check when UE received RRCReconfiguration message for handover

Some IEs can be absent in RRCReconfiguration message for handover, the configuration is valid for COTS UE to finish handover.
This commit fixes some null pointer dereferencing that will cause segmentation fault.

openair2/LAYER2/NR_MAC_UE/config_ue.c

@@ -262,8 +262,9 @@ static void config_common_ue_sa(NR_UE_MAC_INST_t *mac, NR_ServingCellConfigCommo
                                                                 mac->frequency_range);
     //prach_fd_occasion->num_unused_root_sequences = ???
   }
-  cfg->prach_config.ssb_per_rach = rach_ConfigCommon->ssb_perRACH_OccasionAndCB_PreamblesPerSSB->present-1;
-
+  if (rach_ConfigCommon->ssb_perRACH_OccasionAndCB_PreamblesPerSSB) {
+    cfg->prach_config.ssb_per_rach = rach_ConfigCommon->ssb_perRACH_OccasionAndCB_PreamblesPerSSB->present - 1;
+  }
 }
 
 // computes round-trip-time between ue and sat based on SIB19 ephemeris data
@@ -547,7 +548,9 @@ static void config_common_ue(NR_UE_MAC_INST_t *mac, NR_ServingCellConfigCommon_t
       prach_fd_occasion->num_root_sequences =
           compute_nr_root_seq(rach_ConfigCommon, nb_preambles, frame_type, mac->frequency_range);
 
-      cfg->prach_config.ssb_per_rach = rach_ConfigCommon->ssb_perRACH_OccasionAndCB_PreamblesPerSSB->present - 1;
+      if (rach_ConfigCommon->ssb_perRACH_OccasionAndCB_PreamblesPerSSB) {
+        cfg->prach_config.ssb_per_rach = rach_ConfigCommon->ssb_perRACH_OccasionAndCB_PreamblesPerSSB->present - 1;
+      }
       // prach_fd_occasion->num_unused_root_sequences = ???
     }
   }
@@ -914,6 +917,12 @@ static void nr_configure_lc_config(NR_UE_MAC_INST_t *mac,
 static nr_lcid_rb_t configure_lcid_rb(NR_RLC_BearerConfig_t *rlc_bearer)
 {
   nr_lcid_rb_t rb;
+  if (!rlc_bearer->servedRadioBearer) {
+    LOG_W(NR_MAC, "RLC bearer config does not contain servedRadioBearer.\n");
+    rb.type = NR_LCID_NONE;
+    return rb;
+  }
+
   if (rlc_bearer->servedRadioBearer->present == NR_RLC_BearerConfig__servedRadioBearer_PR_srb_Identity) {
     rb.type = NR_LCID_SRB;
     rb.choice.srb_id = rlc_bearer->servedRadioBearer->choice.srb_Identity;