Flutter null safety – The argument type 'Color?' can't be assigned to the parameter type 'Color'

Issue

I changed my SDK version for flutter to min , so that I can fix my code for null safety.

There is one issue that I don’t understand,
this line produces the following error:

The argument type 'Color?' can't be assigned to the parameter type 'Color'

border: Border.all(color: Colors.grey[300], width: 1),

but if I change Colors.grey[300] with whatever value that doesn’t use [], it will work,
so Colors.grey works perfectly fine.

What should I change here to keep using grey[300]?

You can use 0xFFE0E0E0 for grey[300].

To pick material colors you can use this tool.

To select a specific color from one of the swatches, index into the swatch using an integer for the specific color desired, as follows:

Color selection = Colors.green[400]!; // Selects a mid-range green.

Each ColorSwatch constant is a color and can used directly. For example:

Container(
  color: Colors.blue, // same as Colors.blue[500] or Colors.blue.shade500
)

Answered By – Simon Sot