GradientColors constructor Null safety
Implementation
const GradientColors(this.startColor, this.endColor)
: assert(startColor != null),
assert(endColor != null),
super(ZowieColorType.gradient);
const GradientColors(this.startColor, this.endColor)
: assert(startColor != null),
assert(endColor != null),
super(ZowieColorType.gradient);