[Bug] [FA] [1.21.1] [CMP] NullPointerException: Cannot Invoke "net.createmod.catnip.data.Pair.getSecond()" Because "pair" Is Null

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This article addresses a critical bug encountered in Create: Mobile Packages version 1.21.1, specifically when using the Portable Stock Ticker (PST) from the Create mod without Factory Logistics (FL) installed. This NullPointerException can disrupt gameplay by preventing packages from being sent, severely impacting logistical operations within the Create mod ecosystem. This comprehensive guide provides a detailed explanation of the issue, the steps to reproduce it, and a deep dive into the error logs, aiming to assist both users encountering the problem and developers seeking to resolve it. Understanding the intricacies of this bug is crucial for maintaining a smooth and efficient experience with Create: Mobile Packages. The NullPointerException arises due to the interaction between Create: Mobile Packages and Create Factory Abstractions, particularly when Factory Logistics is absent. This results in a failure to properly handle package requests, leading to the error and preventing package transmission. This issue highlights the importance of dependency management in modded environments and the need for robust error handling to prevent such crashes. By carefully analyzing the error logs and the steps to reproduce the bug, we can gain valuable insights into the underlying mechanisms and potential solutions.

Users of Create: Mobile Packages 1.21.1 are encountering a NullPointerException when attempting to send packages using the Portable Stock Ticker (PST). This issue occurs specifically when the Factory Logistics (FL) mod is not installed. The error manifests as a server-side crash, preventing the package from being sent and disrupting gameplay. This NullPointerException is a critical bug that affects the functionality of the Portable Stock Ticker, a key component in the Create: Mobile Packages mod. The PST allows players to remotely manage and send packages, making it an essential tool for logistical operations. When this functionality is compromised due to the error, players are unable to efficiently transport items and resources, which can significantly impact their gameplay experience. The issue is triggered by a failure to properly handle package requests when Factory Logistics is not present, indicating a potential dependency or compatibility issue between the mods. This bug underscores the importance of thorough testing in different mod configurations to ensure that all features function as expected. Addressing this issue promptly is crucial for maintaining the stability and usability of Create: Mobile Packages. The NullPointerException not only disrupts gameplay but also affects the user's overall satisfaction with the mod. By identifying and resolving the root cause of this error, developers can enhance the mod's reliability and ensure a smoother experience for all players. This detailed description of the issue aims to provide a clear understanding of the problem, facilitating the troubleshooting process and helping users avoid the bug until a fix is available.

Error Log Snippet

[20:27:31] [Server thread/ERROR] [minecraft/BlockableEventLoop]: Error executing task on Server
java.util.concurrent.CompletionException: java.lang.NullPointerException: Cannot invoke "net.createmod.catnip.data.Pair.getSecond()" because "pair" is null
	at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:315) ~[?:?] {re:mixin}
	at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:320) ~[?:?] {re:mixin}
	at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run$$capture(CompletableFuture.java:1770) ~[?:?] {}
	at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java) ~[?:?] {}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.TickTask.run(TickTask.java:18) ~[neoforge-21.1.159.jar%23183!/:?] {re:classloading}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:151) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,re:computing_frames,re:classloading}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:881) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:170) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:122) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:864) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:858) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:135) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.managedBlock(MinecraftServer.java:830) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.waitUntilNextTick(MinecraftServer.java:835) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:718) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:267) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:ponder-common.mixins.json:accessor.MinecraftServerAccessor from mod ponder,pl:mixin:A}
	at java.base/java.lang.Thread.run(Thread.java:1583) [?:?] {}
Caused by: java.lang.NullPointerException: Cannot invoke "net.createmod.catnip.data.Pair.getSecond()" because "pair" is null
	at TRANSFORMER/create_factory_abstractions@1.4.3/ru.zznty.create_factory_abstractions.generic.support.LogisticallyLinkedGenericBehaviour$1.processRequest(LogisticallyLinkedGenericBehaviour.java:38) ~[create_factory_abstractions-1.21.1-1.4.3.jar%23187!/:1.4.3] {re:classloading}
	at TRANSFORMER/create_factory_abstractions@1.4.3/ru.zznty.create_factory_abstractions.generic.support.GenericLogisticsManager.findPackagersForRequest(GenericLogisticsManager.java:70) ~[create_factory_abstractions-1.21.1-1.4.3.jar%23187!/:1.4.3] {re:classloading}
	at TRANSFORMER/create_factory_abstractions@1.4.3/ru.zznty.create_factory_abstractions.generic.support.GenericLogisticsManager.broadcastPackageRequest(GenericLogisticsManager.java:25) ~[create_factory_abstractions-1.21.1-1.4.3.jar%23187!/:1.4.3] {re:classloading}
	at TRANSFORMER/create_mobile_packages@0.5.3/de.theidler.create_mobile_packages.items.portable_stock_ticker.StockCheckingItem.broadcastPackageRequest(StockCheckingItem.java:54) ~[%23185!/:?] {re:classloading}
	at TRANSFORMER/create_mobile_packages@0.5.3/de.theidler.create_mobile_packages.items.portable_stock_ticker.PortableStockTicker.broadcastPackageRequest(PortableStockTicker.java:58) ~[%23185!/:?] {re:classloading}
	at TRANSFORMER/create_mobile_packages@0.5.3/de.theidler.create_mobile_packages.items.portable_stock_ticker.SendPackage.applySettings(SendPackage.java:46) ~[%23185!/:?] {re:classloading}
	at TRANSFORMER/create_mobile_packages@0.5.3/de.theidler.create_mobile_packages.items.portable_stock_ticker.SendPackage.handle(SendPackage.java:57) ~[%23185!/:?] {re:classloading}
	at TRANSFORMER/ponder@1.0.56/net.createmod.catnip.platform.NeoForgeNetworkHelper.lambda$registerPackets$2(NeoForgeNetworkHelper.java:48) ~[Ponder-NeoForge-1.21.1-1.0.56.jar%23189!/:1.0.56] {re:classloading}
	at TRANSFORMER/neoforge@21.1.159/net.neoforged.neoforge.network.handling.ServerPayloadContext.enqueueWork(ServerPayloadContext.java:32) ~[neoforge-21.1.159.jar%23184!/:?] {re:classloading}
	at TRANSFORMER/ponder@1.0.56/net.createmod.catnip.platform.NeoForgeNetworkHelper.lambda$registerPackets$3(NeoForgeNetworkHelper.java:47) ~[Ponder-NeoForge-1.21.1-1.0.56.jar%23189!/:1.0.56] {re:classloading}
	at TRANSFORMER/neoforge@21.1.159/net.neoforged.neoforge.network.handling.MainThreadPayloadHandler.lambda$handle$0(MainThreadPayloadHandler.java:16) ~[neoforge-21.1.159.jar%23184!/:?] {re:classloading}
	at TRANSFORMER/minecraft@1.21.1/net.minecraft.util.thread.BlockableEventLoop.lambda$submitAsync$0(BlockableEventLoop.java:60) ~[neoforge-21.1.159.jar%23183!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
	at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run$$capture(CompletableFuture.java:1768) ~[?:?] {}
	... 15 more

The provided error log snippet offers a detailed view into the NullPointerException occurring within Create: Mobile Packages. The core of the issue lies in the line Cannot invoke "net.createmod.catnip.data.Pair.getSecond()" because "pair" is null. This indicates that the code is attempting to access the second element of a Pair object, but the Pair object itself is null. This null value is causing the program to crash, as it cannot perform the requested operation on a non-existent object. The stack trace reveals that the error originates in the LogisticallyLinkedGenericBehaviour$1.processRequest method within the create_factory_abstractions mod. This method is part of the logic that handles package requests, and its failure suggests a problem in how package requests are being processed when Factory Logistics is not installed. The error propagates through several layers of the code, eventually leading to the crash on the server thread. This comprehensive stack trace allows developers to pinpoint the exact location of the bug and understand the sequence of events that lead to the NullPointerException. By tracing the method calls and examining the data flow, it becomes possible to identify the conditions under which the Pair object becomes null. This information is crucial for developing a fix that addresses the root cause of the issue. The involvement of multiple mods, including create_factory_abstractions, create_mobile_packages, and ponder, highlights the complexity of modded environments and the importance of ensuring compatibility between different mods. Analyzing the interactions between these mods is essential for resolving the bug and preventing similar issues in the future.

  1. Install Create: Mobile Packages 1.21.1 and Create Factory Abstractions 1.4.3 in your Minecraft instance.
  2. Ensure that Factory Logistics (FL) is NOT installed. This is the key condition for triggering the bug.
  3. Obtain a Portable Stock Ticker (PST) from Create: Mobile Packages.
  4. Bind the PST to a suitable inventory or logistics network.
  5. Open the PST interface.
  6. Attempt to send a package using the PST.
  7. Observe the server-side error and the failure of the package to be sent.

These steps provide a clear and concise method for reproducing the NullPointerException in Create: Mobile Packages. The critical aspect of these steps is the explicit instruction to ensure that Factory Logistics (FL) is NOT installed. This condition is the primary trigger for the bug, as the code within Create: Mobile Packages and Create Factory Abstractions behaves differently when FL is absent. By following these steps, users can reliably reproduce the error and confirm that they are experiencing the same issue. This reproducibility is essential for bug reporting and allows developers to verify the fix once it is implemented. The process involves interacting with the Portable Stock Ticker (PST), a central feature of Create: Mobile Packages. The PST's functionality is directly affected by the bug, making it the focal point of the reproduction steps. Binding the PST to an inventory or logistics network is a necessary prerequisite for sending packages, ensuring that the setup accurately reflects a typical use case. Attempting to send a package through the PST triggers the underlying code that is susceptible to the NullPointerException. Observing the server-side error is the final confirmation that the bug has been successfully reproduced. This detailed set of steps ensures that users can consistently encounter the issue, providing valuable information for troubleshooting and debugging. By clearly outlining the environment and actions required to trigger the bug, these steps contribute to a more efficient resolution process.

The root cause of this NullPointerException lies in the interaction between Create: Mobile Packages and Create Factory Abstractions when Factory Logistics (FL) is not present. The error message Cannot invoke "net.createmod.catnip.data.Pair.getSecond()" because "pair" is null indicates that a Pair object, which is expected to contain two elements, is null when the code attempts to access its second element. This typically occurs when a function or method that is supposed to return a Pair object fails to do so under certain conditions, resulting in a null return value. In this specific case, the LogisticallyLinkedGenericBehaviour$1.processRequest method in Create Factory Abstractions is the source of the error. This method likely relies on functionality provided by Factory Logistics to handle package requests. When FL is not installed, this functionality is missing, and the method fails to return a valid Pair object, leading to the null value. The subsequent attempt to access the second element of this null Pair object triggers the NullPointerException. This analysis highlights a potential dependency issue between Create: Mobile Packages, Create Factory Abstractions, and Factory Logistics. It suggests that the code in Create: Mobile Packages and/or Create Factory Abstractions does not adequately handle the scenario where FL is not installed. This could be due to a missing null check or an incorrect assumption about the availability of FL's functionality. To fix this bug, developers need to identify the exact conditions under which the Pair object becomes null and implement appropriate error handling. This might involve adding a null check before accessing the Pair object's elements or providing an alternative mechanism for handling package requests when FL is not installed. Addressing this root cause will ensure that Create: Mobile Packages functions correctly even without Factory Logistics, preventing future occurrences of this NullPointerException.

Several potential solutions can address the NullPointerException encountered when using Create: Mobile Packages without Factory Logistics (FL). These solutions focus on handling the absence of FL's functionality and preventing the null Pair object from causing a crash. Here are some key approaches:

  1. Implement Null Checks: The most straightforward solution is to add null checks before accessing the elements of the Pair object within the LogisticallyLinkedGenericBehaviour$1.processRequest method. This would prevent the NullPointerException by ensuring that the code only attempts to access the second element if the Pair object is not null. This approach involves adding a simple if statement to check if the pair variable is null before calling pair.getSecond(). If pair is null, the code can either return a default value or skip the operation entirely, avoiding the crash. This solution is relatively easy to implement and can quickly address the immediate issue.
  2. Provide Alternative Logic: When Factory Logistics is not installed, the code can follow an alternative path for handling package requests. This might involve using a different mechanism for finding packagers or skipping certain steps that rely on FL's functionality. This solution requires a deeper understanding of the code's logic and the role of Factory Logistics in the package request process. By identifying the specific functions and methods that depend on FL, developers can create alternative implementations that function without it. This could involve using a simpler algorithm for finding packagers or directly accessing inventories without going through the FL logistics network. This approach ensures that Create: Mobile Packages remains functional even when FL is not present, providing a more robust and flexible solution.
  3. Declare Factory Logistics as a Dependency: If Create: Mobile Packages is designed to function optimally with Factory Logistics, explicitly declaring FL as a dependency can prevent this issue. This would ensure that users are aware of the required mod and install it accordingly. This solution is more of a preventive measure than a direct fix for the NullPointerException. By declaring FL as a dependency, the mod loader will ensure that FL is installed before Create: Mobile Packages, eliminating the condition that triggers the bug. This approach simplifies the mod installation process for users and reduces the likelihood of encountering compatibility issues. However, it also means that Create: Mobile Packages cannot be used without FL, which might not be desirable for all users. Therefore, this solution should be considered carefully based on the intended use case and the mod's design philosophy.
  4. Throw a Custom Exception: Instead of a NullPointerException, throwing a custom exception that provides more context about the error can aid in debugging and user understanding. This custom exception can indicate that Factory Logistics is required for this functionality. This approach improves the error handling in Create: Mobile Packages by providing more informative error messages. When the code encounters the condition that would lead to a NullPointerException, it can throw a custom exception with a message explaining that Factory Logistics is required. This makes it easier for both users and developers to understand the issue and take appropriate action. For example, the error message could instruct the user to install Factory Logistics or suggest an alternative way to achieve the same goal without FL. This solution enhances the user experience by providing clear and actionable feedback.

These potential solutions offer a range of options for addressing the NullPointerException in Create: Mobile Packages. The choice of solution will depend on the specific design goals of the mod and the desired level of compatibility with other mods. Implementing null checks is a quick and easy fix, while providing alternative logic offers a more robust solution that allows the mod to function without Factory Logistics. Declaring FL as a dependency prevents the issue entirely but might limit the mod's usability in certain scenarios. Throwing a custom exception improves error handling and provides more informative error messages. By carefully considering these options, developers can choose the solution that best fits their needs and ensures a smooth and reliable experience for users of Create: Mobile Packages.

The NullPointerException in Create: Mobile Packages significantly impacts user experience by disrupting the functionality of the Portable Stock Ticker (PST). When users attempt to send packages using the PST without Factory Logistics (FL) installed, the server crashes, preventing the package from being sent. This not only frustrates players but also hinders their ability to manage logistics and transport items efficiently. The impact is particularly pronounced in multiplayer environments, where coordinated logistics are crucial for gameplay. A server crash can disrupt the entire game, affecting all players and potentially leading to loss of progress. The NullPointerException can also be confusing for users who may not understand the underlying cause of the error. The generic error message does not clearly indicate the missing dependency on Factory Logistics, making it difficult for players to troubleshoot the issue on their own. This can lead to frustration and a negative perception of the mod. Furthermore, the bug can discourage players from using the Portable Stock Ticker, a key feature of Create: Mobile Packages. If users encounter frequent crashes when attempting to send packages, they may opt to use alternative methods for item transport, diminishing the value of the mod. The NullPointerException can also have a ripple effect on other mods that rely on Create: Mobile Packages for logistics. If the PST is not functioning correctly, it can disrupt the flow of items and resources in interconnected systems, potentially causing further issues. To mitigate the negative impact of this bug, it is essential to provide clear and informative error messages that guide users towards a solution. This could involve displaying a message that explicitly states the requirement for Factory Logistics when the error occurs. Additionally, addressing the root cause of the NullPointerException by implementing null checks or providing alternative logic will ensure a more stable and reliable experience for users of Create: Mobile Packages. Ultimately, resolving this issue will enhance the overall user experience and encourage players to fully utilize the features of the mod.

The NullPointerException encountered in Create: Mobile Packages 1.21.1 when using the Portable Stock Ticker without Factory Logistics installed is a significant issue that disrupts gameplay and hinders the mod's functionality. This bug, characterized by the error message Cannot invoke "net.createmod.catnip.data.Pair.getSecond()" because "pair" is null, stems from a failure to handle package requests properly when FL is absent. The detailed analysis presented in this article highlights the root cause of the error, which lies in the interaction between Create: Mobile Packages and Create Factory Abstractions. The absence of Factory Logistics leads to a null Pair object, triggering the NullPointerException when the code attempts to access its second element. Several potential solutions have been discussed, ranging from implementing null checks and providing alternative logic to declaring Factory Logistics as a dependency and throwing custom exceptions. Each solution offers a different approach to addressing the issue, with varying levels of complexity and impact on the mod's design. The impact of this bug on user experience is substantial, as it prevents players from using the Portable Stock Ticker effectively and can lead to server crashes in multiplayer environments. Addressing this issue is crucial for ensuring a smooth and enjoyable gameplay experience for users of Create: Mobile Packages. By implementing one or more of the proposed solutions, developers can mitigate the NullPointerException and restore the functionality of the PST. Furthermore, this bug serves as a valuable reminder of the importance of thorough testing in different mod configurations and the need for robust error handling to prevent unexpected crashes. Resolving this NullPointerException will not only enhance the stability of Create: Mobile Packages but also improve its overall usability and user satisfaction. This detailed examination of the bug provides a comprehensive understanding of the issue and offers practical guidance for developers seeking to implement a fix. Ultimately, addressing this problem will contribute to a more robust and reliable modding ecosystem for Minecraft players.