Added a few null checks.

code/modules/organs/organ_external.dm

@@ -3,13 +3,16 @@
 ****************************************************/
 /obj/item/organ/external
 	name = "external"
+	min_broken_damage = 30
+	max_damage = 0
+	dir = SOUTH
+	organ_tag = "limb"
+
 	var/icon_name = null
 	var/body_part = null
 	var/icon_position = 0
-
 	var/model
 	var/force_icon
-
 	var/damage_state = "00"
 	var/brute_dam = 0
 	var/burn_dam = 0
@@ -26,38 +29,25 @@
 	var/list/wounds = list()
 	var/number_wounds = 0 // cache the number of wounds, which is NOT wounds.len!
 	var/perma_injury = 0
-
 	var/obj/item/organ/external/parent
 	var/list/obj/item/organ/external/children
-
-	// Internal organs of this body part
-	var/list/internal_organs = list()
-
+	var/list/internal_organs = list() 	// Internal organs of this body part
 	var/damage_msg = "\red You feel an intense pain"
 	var/broken_description
-
 	var/open = 0
 	var/stage = 0
 	var/cavity = 0
 	var/sabotaged = 0 // If a prosthetic limb is emagged, it will detonate when it fails.
 	var/encased       // Needs to be opened with a saw to access the organs.
-
 	var/obj/item/hidden = null
 	var/list/implants = list()
-
-	// how often wounds should be updated, a higher number means less often
-	var/wound_update_accuracy = 1
-
+	var/wound_update_accuracy = 1 	// how often wounds should be updated, a higher number means less often
 	var/joint = "joint"   // Descriptive string used in dislocation.
 	var/amputation_point  // Descriptive string used in amputation.
 	var/dislocated = 0    // If you target a joint, you can dislocate the limb, causing temporary damage to the organ.
 	var/can_grasp
 	var/can_stand
 
-	min_broken_damage = 30
-	max_damage = 0
-	dir = SOUTH
-
 /obj/item/organ/external/attackby(obj/item/weapon/W as obj, mob/user as mob)
 	switch(stage)
 		if(0)

code/modules/projectiles/targeting.dm

@@ -23,7 +23,7 @@
 //Removing the lock and the buttons.
 /obj/item/weapon/gun/dropped(mob/user as mob)
 	stop_aim()
-	if (user.client)
+	if(user && user.client)
 		user.client.remove_gun_icons()
 	return ..()
 
@@ -47,7 +47,7 @@
 /obj/item/weapon/gun/proc/PreFire(atom/A as mob|obj|turf|area, mob/living/user as mob|obj, params)
 	//Lets not spam it.
 	if(lock_time > world.time - 2) return
-	
+
 	user.set_dir(get_cardinal_dir(src, A))
 	if(isliving(A) && !(A in aim_targets))
 		Aim(A) 	//Clicked a mob, aim at them
@@ -58,7 +58,7 @@
 	if(isliving(M) && (M in view(user)) && !(M in aim_targets))
 		Aim(M) //Aha!  Aim at them!
 		return 1
-	
+
 	return 0
 
 //Aiming at the target mob.
@@ -83,12 +83,12 @@
 	if(src != M.get_active_hand())
 		stop_aim()
 		return
-	
+
 	//reflex firing is disabled when help intent is set
 	if (M.a_intent == I_HELP)
 		M << "\red You refrain from firing your [src] as your intent is set to help."
 		return
-	
+
 	M.last_move_intent = world.time
 	var/firing_check = can_hit(T,usr) //0 if it cannot hit them, 1 if it is capable of hitting, and 2 if a special check is preventing it from firing.
 	if(firing_check > 0)

code/modules/surgery/organs_internal.dm

@@ -343,9 +343,11 @@
 		var/o_a =  (O.gender == PLURAL) ? "" : "a "
 		var/o_do = (O.gender == PLURAL) ? "don't" : "doesn't"
 
-		if(target.species.has_organ[O.organ_tag])
+		if(O.organ_tag == "limb")
+			return 0
+		else if(target.species.has_organ[O.organ_tag])
 
-			if(!O.health)
+			if(O.is_damaged())
 				user << "\red \The [O.organ_tag] [o_is] in no state to be transplanted."
 				return 2