code: @Nullable
  	public static String concatenateWithAnd(@Nullable String s1, @Nullable String s2) {
  		if (s1 != null) {
  			return s2 == null ? s1 : s1 + " and " + s2;
  		}
  		else {
  			return s2;
  		}
  	}
docs: If both string arguments are non-null, this method concatenates them with ' and '.
  If only one of the arguments is non-null, this method returns the non-null argument.
  If both arguments are null, this method returns null.
  
  @param s1 The first string argument
  @param s2 The second string argument
  
  @return The concatenated string, or non-null argument, or null