Assert.Null - jnm2/nunit-docs-wiki GitHub Wiki
Assert.Null and Assert.IsNull test that the specified object is null. The two forms are provided for compatibility with past versions of NUnit and NUnitLite.
Assert.Null(object anObject);
Assert.Null(object anObject, string message, params object[] parms);
Assert.IsNull(object anObject);
Assert.IsNull(object anObject, string message, params object[] parms);