[2.51.0] midx-write: fix segfault and other cleanups - #787

The target framework 'netcoreapp3.1' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.

The target framework 'netcoreapp3.1' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.