[Fixed] World Partition HLOD Build = Assertion failed: Pair != nullptr

Development World Creation
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1

The following error is put out in 5.3.2 when building HLODs in a WorldPartition environment:

LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.55:154][  5]LogWindows: Error: appError called: Assertion failed: Pair != nullptr [File:F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Core\Public\Containers\Map.h] [Line: 671] 
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.55:155][  5]LogWindows: Error: Windows GetLastError: The handle is invalid. (6)
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:519][  5]LogWindows: Error: === Critical error: ===
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:519][  5]LogWindows: Error: 
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:519][  5]LogWindows: Error: Assertion failed: Pair != nullptr [File:F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Core\Public\Containers\Map.h] [Line: 671] 
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:519][  5]LogWindows: Error: 
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:519][  5]LogWindows: Error: 
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:519][  5]LogWindows: Error: 
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:519][  5]LogWindows: Error: [Callstack] 0x00007ff86a5ebfae UnrealEditor-Landscape.dll!ALandscapeProxy::ExportToRawMeshDataCopyNew() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Landscape\Private\LandscapeEdit.cpp:4187]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:520][  5]LogWindows: Error: [Callstack] 0x00007ff86a5e84ce UnrealEditor-Landscape.dll!ALandscapeProxy::ExportToRawMesh() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Landscape\Private\LandscapeEdit.cpp:3846]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:520][  5]LogWindows: Error: [Callstack] 0x00007ff86a716472 UnrealEditor-Landscape.dll!ULandscapeHLODBuilder::Build() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Landscape\Private\LandscapeHLODBuilder.cpp:287]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:520][  5]LogWindows: Error: [Callstack] 0x00007ff8711b4858 UnrealEditor-Engine.dll!UHLODBuilder::Build() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Engine\Private\WorldPartition\HLOD\HLODBuilder.cpp:317]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:520][  5]LogWindows: Error: [Callstack] 0x0000022b758315fd UnrealEditor-WorldPartitionHLODUtilities.dll!FWorldPartitionHLODUtilities::BuildHLOD() [F:\UE\Engine\UE_5.3_Source\Engine\Plugins\Editor\WorldPartitionHLODUtilities\Source\Private\WorldPartition\HLOD\Utilities\WorldPartitionHLODUtilities.cpp:720]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:521][  5]LogWindows: Error: [Callstack] 0x00007ff8711b5add UnrealEditor-Engine.dll!AWorldPartitionHLOD::BuildHLOD() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Engine\Private\WorldPartition\HLOD\HLODActor.cpp:424]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:521][  5]LogWindows: Error: [Callstack] 0x00007ff86c459a1e UnrealEditor-UnrealEd.dll!UWorldPartitionHLODsBuilder::BuildHLODActors() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Editor\UnrealEd\Private\WorldPartition\WorldPartitionHLODsBuilder.cpp:504]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:521][  5]LogWindows: Error: [Callstack] 0x00007ff86c4909c8 UnrealEditor-UnrealEd.dll!UWorldPartitionHLODsBuilder::RunInternal() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Editor\UnrealEd\Private\WorldPartition\WorldPartitionHLODsBuilder.cpp:305]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:522][  5]LogWindows: Error: [Callstack] 0x00007ff86c48f515 UnrealEditor-UnrealEd.dll!UWorldPartitionBuilder::Run() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Editor\UnrealEd\Private\WorldPartition\WorldPartitionBuilder.cpp:279]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:522][  5]LogWindows: Error: [Callstack] 0x00007ff86c490046 UnrealEditor-UnrealEd.dll!UWorldPartitionBuilder::RunBuilder() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Editor\UnrealEd\Private\WorldPartition\WorldPartitionBuilder.cpp:116]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:522][  5]LogWindows: Error: [Callstack] 0x00007ff86b3fae82 UnrealEditor-UnrealEd.dll!UWorldPartitionBuilderCommandlet::RunBuilder() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Editor\UnrealEd\Private\Commandlets\WorldPartitionBuilderCommandlet.cpp:229]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:522][  5]LogWindows: Error: [Callstack] 0x00007ff86b3d3885 UnrealEditor-UnrealEd.dll!UWorldPartitionBuilderCommandlet::Main() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Editor\UnrealEd\Private\Commandlets\WorldPartitionBuilderCommandlet.cpp:128]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:523][  5]LogWindows: Error: [Callstack] 0x00007ff75589733f UnrealEditor.exe!FEngineLoop::PreInitPostStartupScreen() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Launch\Private\LaunchEngineLoop.cpp:4136]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:523][  5]LogWindows: Error: [Callstack] 0x00007ff75588cfb6 UnrealEditor.exe!GuardedMain() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Launch\Private\Launch.cpp:140]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:523][  5]LogWindows: Error: [Callstack] 0x00007ff75588d37a UnrealEditor.exe!GuardedMainWrapper() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:118]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:535][  5]LogWindows: Error: [Callstack] 0x00007ff755890854 UnrealEditor.exe!LaunchWindowsStartup() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:258]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:535][  5]LogWindows: Error: [Callstack] 0x00007ff7558a6984 UnrealEditor.exe!WinMain() [F:\UE\Engine\UE_5.3_Source\Engine\Source\Runtime\Launch\Private\Windows\LaunchWindows.cpp:298]
LogWorldPartitionEditor: Error:   #### COMMANDLET OUTPUT >> [2024.04.19-20.54.56:535][  5]LogWindows: Error: [Callstack] 0x00007ff7558a9d7a UnrealEditor.exe!__scrt_common_main_seh() [D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288]
2

This is caused when the spatially loaded landscape has HLOD enabled (which is set per default by the Engine).

The documentation states

Some world components, such as Landscapes and Water components, are currently not supported by HLOD Actors. World Partition - Hierarchical Level of Detail in Unreal Engine

Thus, the above error can be fixed by unchecking the default HLOD setting for all landscape partitions (tiles). This is a confusing error because you do not expect the engine to set the HLOD on the landscape when it is not supported and results in a critical error.