Something more about runtime errors.

code/modules/mob/living/carbon/human/human.dm

@@ -834,7 +834,7 @@
 	..()
 
 /mob/living/carbon/human/vomit(lost_nutrition = 10, blood = 0, stun = 1, distance = 0, message = 1, toxic = 0)
-	if(blood && (NOBLOOD in dna.species.species_traits))
+	if(blood && dna?.species && (NOBLOOD in dna.species.species_traits))
 		if(message)
 			visible_message("<span class='warning'>[src] dry heaves!</span>", \
 							"<span class='userdanger'>You try to throw up, but there's nothing in your stomach!</span>")

code/modules/mob/living/carbon/human/human_defense.dm

@@ -20,7 +20,7 @@
 
 
 /mob/living/carbon/human/proc/checkarmor(obj/item/bodypart/def_zone, d_type)
-	if(!d_type)
+	if(!d_type || !def_zone)
 		return 0
 	var/protection = 0
 	var/list/body_parts = list(head, wear_mask, wear_suit, w_uniform, back, gloves, shoes, belt, s_store, glasses, ears, wear_id, wear_neck) //Everything but pockets. Pockets are l_store and r_store. (if pockets were allowed, putting something armored, gloves or hats for example, would double up on the armor)

code/modules/mob/living/carbon/inventory.dm

@@ -72,7 +72,7 @@
 			put_in_hands(I)
 			update_inv_hands()
 		if(SLOT_IN_BACKPACK)
-			if(!SEND_SIGNAL(back, COMSIG_TRY_STORAGE_INSERT, I, src, TRUE))
+			if(!back || !SEND_SIGNAL(back, COMSIG_TRY_STORAGE_INSERT, I, src, TRUE))
 				not_handled = TRUE
 		else
 			not_handled = TRUE