Make the on_hit field optional

README.md

@@ -61,7 +61,7 @@ Definition: definition table, containing:
   * target (optional, defaulting to throwing.target_both): what the arrow is able to hit (throwing.target_node, throwing.target_object, throwing.target_both).
   * allow_protected (optional, defaulting to false): whether the arrow can be throw in a protected area
   * on_hit_sound (optional): sound played when the arrow hits a node or an object.
-  * on_hit(pos, last_pos, node, object, hitter, data, self) (must exist, will crash if nil): callback function:
+  * on_hit(pos, last_pos, node, object, hitter, data, self) (optional but very useful): callback function:
     - pos: the position of the hit node or object.
     - last_pos: the last air node where the arrow was
     - node and object: hit node or object. Either node or object is nil, depending

init.lua

@@ -111,16 +111,18 @@ local function arrow_step(self, dtime)
 			return
 		end
 
-		local ret, reason = self.on_hit(pos, self.last_pos, node, obj, player, self.data, self)
-		if ret == false then
-			if reason then
-				logging(": on_hit function failed for reason: "..reason)
-			else
-				logging(": on_hit function failed")
-			end
+		if self.on_hit then
+			local ret, reason = self.on_hit(pos, self.last_pos, node, obj, player, self.data, self)
+			if ret == false then
+				if reason then
+					logging(": on_hit function failed for reason: "..reason)
+				else
+					logging(": on_hit function failed")
+				end
 
-			hit_failed()
-			return
+				hit_failed()
+				return
+			end
 		end
 
 		if self.on_hit_sound then