Question Mark (?) after session variable reference – What does that mean

I have had a code snippet comes to modify. In there i found this such syntax.

Session("LightBoxID")?.ToString()

I didn’t understand what is that Question mark (?) there means. No googling helped me about any hint

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Answers:

Method 1

Method 2

Answers:

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Method 1

It’s the Null-Conditional Operator
It’s a syntactic sugar for null checking:

return str?.ToString();

will become

if (str == null)
{
    return null;
}
return str.ToString();

Method 2

It performs a null-check on Session("LightBoxID") before attempting to call .ToString() on it.

MS Docs: Null-conditional operators ?. and ?[]

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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