[VX] Getting an error when setting an item-based variable

[Space]

I have an event that's supposed to change depending on how much <item name>s the player has in his inventory and it's causing an error in one of the main scripts.
I'm getting it no matter what I set the item to, whether it's an RTP item or a custom one.

[spoiler=Error details]
The Error:

Script 'Game Interpreter' line 750: NoMethodError occurred.
undefined method '[]' for nil:NilClass

The line referenced:

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    when 3  # Item
      value = $game_party.item_number($data_items[@params[4]])
      actor = $game_actors[@parameters[1]]  #THIS ONE
      actor = $game_actors[@params[4]]


The event command causing the error:

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@>Control Variables: [0015: Milk Possessed] = [Milk] in Inventory[/spoiler]

[spoiler=Scripts I'm using that affect items]
Jet's Percentage of Damage Snippet
KGC's Equipment Effects
Modern Algebra's Skill Teaching Equipment & Items
Modern Algebra's Cursed Equipment
KGC's Restored Combat Functions[/spoiler]

Any help solving this will be hugely appreciated :)

[&&&&&&&&&&&&&]

Do you get the error when you try to store the variable, or when you try to pull it?

[Space]

Storing it. I've tried an event that only has that one line in it, and it's giving me the same result D:

[Yeyinde]

Replace that one line with "when 4".  The error is actually a bug with the default scripts in VX.  It should look like this:

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    when 3  # Item
      value = $game_party.item_number($data_items[@params[4]])
    when 4  # Actor
      actor = $game_actors[@params[4]]