Merge two IEnumerables in elegant way [closed]

Answer 1

Just check for null and assign Enumerable.Empty if it is null. This can be done in one step with the null coalescing operator ??

var ienumerable1 = GetEnumerable1() ?? Enumerable.Empty<WhateverType>();
var ienumerable2 = GetEnumerable2() ?? Enumerable.Empty<WhateverType>(); 

return ienumerable1.Union(ienumerable2);

Answer 2

   var ienumerable1 = GetEnumerable1(); 
    var ienumerable2 = GetEnumerable2(); 
    return ienumerable1 != null
                    ? (ienumerable2 != null ? ienumerable1.Union(ienumerable2) : ienumerable1)
                    : ienumerable2;