firstNonNull function

dynamic firstNonNull (dynamic o1, dynamic o2, [ dynamic o3, dynamic o4 ])

Returns the first non-null argument. If all arguments are null, throws an ArgumentError.

Note: if o1 is an Optional, this can be accomplished with o1.or(o2).

Implementation 

firstNonNull(o1, o2, [o3, o4]) {
  if (o1 != null) return o1;
  if (o2 != null) return o2;
  if (o3 != null) return o3;
  if (o4 != null) return o4;
  throw new ArgumentError('All arguments were null');
}