Describe the bug

.NetNano, accessing DegreesCelcuis of a Default(Temperature) throws NotImplemented Exception.

An unhandled exception of type 'System.NotImplementedException' occurred in UnitsNet.Temperature.dll
Additional information: Can not convert 0 to base units.

To Reproduce
Steps to reproduce the behavior (just an example):

1. Create .NetNano project and add UnitsNet.

Execute this code

var x = default(Temperature);
Debug.WriteLine($"{x.DegreesCelsius}");

Behavior

Throws

An unhandled exception of type 'System.NotImplementedException' occurred in UnitsNet.Temperature.dll
Additional information: Can not convert 0 to base units.

Expected behavior

I understand this is a design decision: It wasn't clear that the value is actually a default(Temperature)

If you look at the additional context below, you can see how I bumped into it and the problem that created it.

Maybe a clearer message that the value is a default or unassigned. Does it need an "IsValid" or "IsAssigned" member? Something about "No value assigned to Temperature". Should there be a Temperature.Default member?

Additional context

I found this because another clause assigned its property to default(Temperature) which I stored and tried to access later, resulting in this error.

It just not easy to see or detect that the class is a default(Temperature) and not an actually assigned valid value)