DataRow DisplayName is not generated properly in .NET Framework when using null values

[Mertsch]

Steps to reproduce

Run this test in .NET Framework 4.6.1 mode

[TestClass]
public class UnitTest1
{
    [TestMethod]
    [DataRow("OK", "OK Test")]
    [DataRow("OK1", "OK1 Test")]
    [DataRow(null, " Test")]
    public void TestMethod1(string input, string output)
    {
        Assert.AreEqual(output, $"{input} Test");
    }
}

Expected behavior

Should output the same display name as in .NET Core

Actual behavior

And even worse with multiple null tests

Environment

VS 2017 15.3.5
.NET Core 2.0 / .NET Framework 4.6.1

<package id="MSTest.TestAdapter" version="1.2.0-beta3" targetFramework="net461" />
<package id="MSTest.TestFramework" version="1.2.0-beta3" targetFramework="net461" />

[jayaranigarg]

This is essentially an issue with string.join(String separator, object[] values).

If first value is null like in [DataRow(null, " Test")] , both .net framework and net core used to return an empty string earlier. But this issue got fixed in netcore to return (,Test) refer this. However, it appears that the same fix is not yet ported to .net framework and hence we are observing a difference in behavior.