merge method
Implementation
ButtonStyle? merge(ButtonStyle? other) {
if (other == null) return this;
return ButtonStyle(
textStyle: other.textStyle ?? textStyle,
backgroundColor: other.backgroundColor ?? backgroundColor,
foregroundColor: other.foregroundColor ?? foregroundColor,
shadowColor: other.shadowColor ?? shadowColor,
elevation: other.elevation ?? elevation,
padding: other.padding ?? padding,
shape: other.shape ?? shape,
iconSize: other.iconSize ?? iconSize,
);
}