Dereference of a possibly null reference.

Cannot convert null literal to non-nullable reference type.

'Exception.Exception(SerializationInfo, StreamingContext)' is obsolete: 'This API supports obsolete formatter-based serialization. It should not be called or extended by application code.' (https://aka.ms/dotnet-warnings/SYSLIB0051)

'FieldAttributes.NotSerialized' is obsolete: 'Formatter-based serialization is obsolete and should not be used.'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

'Exception.Exception(SerializationInfo, StreamingContext)' is obsolete: 'This API supports obsolete formatter-based serialization. It should not be called or extended by application code.' (https://aka.ms/dotnet-warnings/SYSLIB0051)

'Exception.Exception(SerializationInfo, StreamingContext)' is obsolete: 'This API supports obsolete formatter-based serialization. It should not be called or extended by application code.' (https://aka.ms/dotnet-warnings/SYSLIB0051)

Cannot convert null literal to non-nullable reference type.

'TypeAttributes.Serializable' is obsolete: 'Formatter-based serialization is obsolete and should not be used.'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

Dereference of a possibly null reference.