How to remove all the null elements inside a generic list in one go?

Question

You'll probably want the following.

List<EmailParameterClass> parameterList = new List<EmailParameterClass>{param1, param2, param3...};
parameterList.RemoveAll(item => item == null);

I do not know of any in-built method, but you could just use linq:

parameterList = parameterList.Where(x => x != null).ToList();

The RemoveAll method should do the trick:

parameterList.RemoveAll(delegate (object o) { return o == null; });

The method OfType() will skip the null values:

List<EmailParameterClass> parameterList =
    new List<EmailParameterClass>{param1, param2, param3...};

IList<EmailParameterClass> parameterList_notnull = 
    parameterList.OfType<EmailParameterClass>();