side property Null safety
The color and weight of the chip's outline.
Defaults to the border side in the ambient ChipThemeData. If the theme border side resolves to null, the default is the border side of shape.
This value is combined with shape to create a shape decorated with an outline. If it is a MaterialStateBorderSide, MaterialStateProperty.resolve is used for the following MaterialStates:
Implementation
BorderSide? get side;