[DotNet] GherkinLine throws NullReferenceException when GetLineText is called on default value

[Code-Grump]

👓 What did you see?

The following exception is thrown:

Message: 
    System.NullReferenceException : Object reference not set to an instance of an object.

Stack Trace: 
    GherkinLine.GetLineText(Int32 indentToRemove)
    Token.GetTokenValue()
    ...

✅ What did you expect to see?

Either:

• A suitable default value such as an empty string or null.
• An exception that indicates it's not valid to call GetLineText(...)

📦 Which tool/library version are you using?

.NET 8 with Gherkin 32.0.0

🔬 How could we reproduce it?

The following snippet demonstrates the problem:

default(GherkinLine).GetLineText(0);

📚 Any additional context?

It looks like a recent change switched GherkinLine from a class to a struct: cf4160f#diff-150d7921f11609b895fc571d0916916563d77bc54d723e6086890c2efb626e34

Structures in C# are stack-initialized and therefore should be valid without a constructor being called - i.e. it should be possible to identify an instance is the default value and handle it appropriately, both as an external caller and in the internal implementation.