Harden Session I/O and migration save flow - #627

Non-nullable field 'MarriageInfo' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the field as nullable.

Non-nullable property 'GuildName' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Parameter 'value' must have a non-null value when exiting with 'true'.

'FormatterServices' is obsolete: 'Formatter-based serialization is obsolete and should not be used.' (https://aka.ms/dotnet-warnings/SYSLIB0050)

Parameter 'value' must have a non-null value when exiting with 'true'.

Parameter 'value' must have a non-null value when exiting with 'true'.

Parameter 'value' must have a non-null value when exiting with 'true'.

Parameter 'value' must have a non-null value when exiting with 'true'.

Parameter 'value' must have a non-null value when exiting with 'true'.