handle empty item slots

lava-collector

@@ -1,12 +1,20 @@
 -- vi: ft=lua
 -- Goal: collect lava using buckets in the nether, deposit the buckets into a fluid transposer that extracts the lava and sends it to a power generator
 
+local function compareItemName(target)
+    local itemDetail = turtle.getItemDetail()
+    if itemDetail == nil then
+        return nil
+    end
+    return itemDetail.name == target
+end
+
 local function isEmptyBucket()
-    return turtle.getItemDetail().name == "minecraft:bucket"
+    compareItemName("minecraft:bucket")
 end
 
 local function isLavaBucket()
-    return turtle.getItemDetail().name == "minecraft:lava_bucket"
+    compareItemName("minecraft:lava_bucket")
 end
 
 local function findFirstEmptyBucket()