public void SelectFromEach4_Source1Null () { IEnumerable<int> s1 = null; IEnumerable<int> s2 = new[]{2}; IEnumerable<int> s3 = new[]{3}; IEnumerable<int> s4 = new[]{4}; s1.SelectFromEach (s2, s3, s4, (a,b,c,d) => ""); }