From 2063566ca27ce564a86d389192b33ca045db15df Mon Sep 17 00:00:00 2001
From: "Clarence \"Sparr\" Risher" <sparr0@gmail.com>
Date: Sat, 22 Aug 2020 19:23:45 -0700
Subject: [PATCH 1/2] Fix crash on blueprint book creation, also refactor
 get_blueprint

---
 util.lua | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/util.lua b/util.lua
index fadba7f..38e5d22 100644
--- a/util.lua
+++ b/util.lua
@@ -4,14 +4,17 @@ local Util = {}
 
 -- Returns the item if it is a blueprint, the selected blueprint in the book if it is a blueprint book, or nil.
 function Util.get_blueprint(bp)
-    if not (bp and bp.valid and bp.valid_for_read) then
-        return nil
-    end
-    if bp.is_blueprint_book and bp.active_index then
-        return Util.get_blueprint(bp.get_inventory(defines.inventory.item_main)[bp.active_index])
-    end
-    if bp.is_blueprint then
-        return bp
+    while (bp and bp.valid and bp.valid_for_read) do
+        if bp.is_blueprint then
+            return bp
+        elseif bp.is_blueprint_book and bp.active_index then
+            local inventory = bp.get_inventory(defines.inventory.item_main)
+            if bp.active_index <= #inventory then
+                bp = inventory[bp.active_index]
+            else
+                return nil
+            end
+        end
     end
     return nil
 end

From 42c7de027c1f8818a847f09780c394107bcbbff2 Mon Sep 17 00:00:00 2001
From: "Clarence \"Sparr\" Risher" <sparr0@gmail.com>
Date: Sat, 22 Aug 2020 22:57:01 -0700
Subject: [PATCH 2/2] Add exit case for get_blueprint refactor

---
 util.lua | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/util.lua b/util.lua
index 38e5d22..c91a4ec 100644
--- a/util.lua
+++ b/util.lua
@@ -14,6 +14,8 @@ function Util.get_blueprint(bp)
             else
                 return nil
             end
+        else
+            return nil
         end
     end
     return nil