Pass nullptr as nullT when creating thread_data to avoid crash #1116

Job	Run time
Disk with PQ / Disk, PQ (ubuntu-latest)	8m 4s
Disk with PQ / Disk, PQ (windows-2019)	10m 46s
Disk with PQ / Disk, PQ (windows-latest)	12m 8s
Dynamic / Dynamic (ubuntu-latest)	6m 13s
Dynamic / Dynamic (windows-2019)	8m 17s
Dynamic / Dynamic (windows-latest)	7m 55s
In-Memory without PQ / In-Mem, Without PQ (ubuntu-latest)	6m 10s
In-Memory without PQ / In-Mem, Without PQ (windows-2019)	9m 4s
In-Memory without PQ / In-Mem, Without PQ (windows-latest)	7m 45s
In-Memory with PQ / In-Mem, PQ (ubuntu-latest)	10m 27s
In-Memory with PQ / In-Mem, PQ (windows-2019)	6m 35s
In-Memory with PQ / In-Mem, PQ (windows-latest)	6m 17s
Labels / Labels (ubuntu-latest)	9m 56s
Labels / Labels (windows-2019)	11m 22s
Labels / Labels (windows-latest)	13m 22s
Python / Python - Ubuntu - cp39-manylinux_x86_64	10m 14s
Python / Python - Ubuntu - cp310-manylinux_x86_64	12m 12s
Python / Python - Ubuntu - cp311-manylinux_x86_64	12m 26s
Unit tests / Unit Tests (ubuntu-latest)	6m 27s
Unit tests / Unit Tests (windows-2019)	7m 36s
Unit tests / Unit Tests (windows-latest)	7m 23s
Python / Python - Windows - cp39-win_amd64	7m 36s
Python / Python - Windows - cp310-win_amd64	7m 16s
Python / Python - Windows - cp311-win_amd64	10m 19s
DiskANN Common Build Checks / Code Formatting Test	14s
DiskANN Common Build Checks / Docker Container Build	6m 1s
	3h 42m 5s

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