IconThemeData copyWith({Color color, double opacity, double size })

Creates a copy of this icon theme but with the given fields replaced with the new values.

Source 

IconThemeData copyWith({ Color color, double opacity, double size }) {
  return new IconThemeData(
    color: color ?? this.color,
    opacity: opacity ?? this.opacity,
    size: size ?? this.size
  );
}