The Error:

    java.lang.NullPointerException: Cannot invoke "java.util.Collection.remove(Object)" because the return value of "java.util.Map.get(Object)" is null

    This is a very common Java error. It means the game's code tried to perform an action (in this case, .remove(Object)) on something that didn't exist (it was null).

    Specifically, it tried to get a list of items (a Collection) from a data storage structure (a Map) using a specific key. However, that key either wasn't in the map, or the list associated with that key was null. Then, it tried to remove an item from this non-existent list, leading to the crash.

What Caused It (The Code Path):

    Description: MousePressed event for BO screen

    XML res loc: minecolonies:gui/citizen/requests.xml (from "-- BO screen mouse event details --")

    This tells us the crash happened when you clicked your mouse (specifically, the left mouse button, GLFW mouse key value: 0) within a MineColonies GUI. The "BO screen" refers to a screen built with the BlockUI library, and the requests.xml points directly to the citizen requests window in MineColonies.

    The crash occurred in com.minecolonies.core.colony.buildings.views.AbstractBuildingView.onRequestedRequestComplete(...). This suggests you clicked a button related to completing or fulfilling a citizen's request.

    The problem seems to be that when trying to process the completion of this request, the mod couldn't find the necessary data (the collection of requests to remove the completed one from).

Key Mods Involved:

    [email protected]: This is the primary mod responsible. The version 1.1.967-1.21.1-snapshot is important. "Snapshot" means it's a development or pre-release version, which is more likely to contain bugs than a stable release.

    [email protected]: This is a library mod that MineColonies (and its dependency Structurize) uses to create its complex GUIs. It's also a "snapshot" version.

    structurize (likely also a snapshot, given the pattern, though not directly in the top lines of the stack trace) is a core dependency for MineColonies.

In Simple Terms:
You clicked a button in the MineColonies citizen request GUI (likely to fulfill a request or similar action). The MineColonies mod then tried to update its internal list of requests for that citizen or building, but it couldn't find the list it was looking for, or the specific request to remove wasn't properly tracked. This caused the game to crash.