Getting a syntax error, ',' expected with TryParse [duplicate]

I'm working on a method to try to get a date from a string.

First I had this code:

public static DateTime? TryGetDate(this string date) 
{
    DateTime? outputDate;

    if(DateTime.TryParse(date, out outputDate)) 
    {
        return outputDate;
    }

    return null;
}

This worked fine but then I saw a suggestion on my Visual Studio telling me to change it to:

public static DateTime? TryGetDate(this string date) 
{
    if(DateTime.TryParse(date, out var outputDate)) 
    {
        return outputDate;
    }

    return null;
}

But after that change, I got a

Syntax error, ',' expected

on the TryParse line of code.

Why did this happen? I got a suggestion with VS but applied that suggestion and I got a compilation error? The project Target Framework version is v4.6.2