https://stackoverflow.com/questions/59336951/message-trying-to-access-array-offset-on-value-of-type-null
The parser php file says the code is from
This is a compressed copy of NBBC. Do not edit!
Copyright (c) 2008-9, the Phantom Inker. All rights reserved.
Portions Copyright (c) 2004-2008 AddedBytes.com
I would hesitate to correct it, but you could alter lines around 1289 to have a fix as in above link.
But I’d suggest you go to a version of php before 7.4 to do the import, and then after import go back to a supported php version
