Using Same browser type from a single file for multiple projects in Selenium C#

Question

I am trying to pass the Browser Type for 45 projects from a single place using Parallel.RunSettings file and adding this file under Test Settings in Visual Studio.
But the value is not being read with NullReferenceException.

Am I missing any step?

Currently we are passing browser type for each project in their respective app.config file but I want to do it from one single place.

Here is my code:

Parallel.runsettings

<?xml version="1.0" encoding="utf-8"?>
<RunSettings>
    <RunConfiguration>
        <MaxCpuCount>4</MaxCpuCount>
    </RunConfiguration>
    <TestRunParameters>
        <Parameter name="browsertype" value="Firefox" />
    </TestRunParameters>
</RunSettings>

Code to Fetch the value:

public string GetBrowser
{
    get
    {
        var value =Convert.ToString(testContext.Properties["browsertype"]);
        return value;
    }
}

//Code To Launch the browser:

if (config.GetBrowser == "Firefox")
{
    this.WebDriver = new FirefoxDriver();
}
else if (config.GetBrowser == "Chrome")
{
    var chromeOptions = new ChromeOptions();
    chromeOptions.AddAdditionalCapability("useAutomationExtension", false);
    this.WebDriver = new ChromeDriver(chromeOptions);
}
else if (config.GetBrowser == "IE")
{
    this.WebDriver = new InternetExplorerDriver();
}