Allow field-based predicates for item searches

items.lua

@@ -63,6 +63,7 @@ function Cache.makeCache(cacheLoader)
 
     local entry = nil
     if #chest.list() == 0 and type(cacheLoader) == "function" then
+      print("Using cacheloader")
       entry = cacheLoader(name, chest)
     end
 
@@ -174,6 +175,10 @@ function Cache:find(predicate)
 end
 
 local function checkField(base, check)
+  if type(base) == "function" then
+    return base(check)
+  end
+  
   local baseType = type(base)
   if baseType == nil then
     return true
@@ -198,10 +203,10 @@ end
 
 function FILTER_MATCHING_SLOTS(target)
   return function(detail)
-    return checkField(target.name, detail.name) and
+    return target == nil or (checkField(target.name, detail.name) and
             checkField(target.displayName, detail.displayName) and
             checkField(target.damage, detail.damage) and
-            checkField(target.enchantments, detail.enchantments)
+            checkField(target.enchantments, detail.enchantments))
   end
 end