code: private static <T> Consumer<T> concat(Consumer<T> a, Consumer<T> b)
  	{
  		if (a != null && b != null) // both non-null
  			return a.andThen(b);
  		else if (a != null)
  			return a;
  		else
  			return b;
  	}
docs: Combine two consumers. Consumers may be null, in which case this selects the non-null one. If both are null then will
  return <code>null</code>
  
  @param a
  the first consumer (optional)
  @param b
  the second consumer (optional)
  @param <T>
  
  @return