[Bug] CustomPacketPayloadWrapper fails to initialize due to wrong reflection usage

[iseal56]

• This issue is not solved in a development build

Describe the bug
CustomPacketPayloadWrapper fails to initialize on 1.21.1

To Reproduce
Steps to reproduce the behavior:

1. Attempt to initialize a CustomPacketPayloadWrapper instance (by doing new CustomPacketPayloadWrapper(...)
2. Notice that when running it crashes because of line 52-62, with this stacktrace

Expected behavior
The CustomPacketPayloadWrapper initializes correctly

Screenshots
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Version Info
5.7.0, and the dump

Additional context
I suppose this is not an issue with my usage in particular as the error happens within the static part of the initializer, particularly when attempting to get the "getPayloadId" method