Gini constructor
Creates a new Gini object with the given year and coefficient.
The year parameter must be greater than 1990, and the coefficient
parameter must be between 0.0 and 100.0 (inclusive).
Implementation
const Gini({required this.year, required this.coefficient})
: assert(year > minYear, "`year` should be greater than $minYear!"),
assert(
coefficient < maxCoefficient,
"`coefficient` should be less than $maxCoefficient!",
),
assert(
coefficient > minCoefficient,
"`coefficient` should be greater than $minCoefficient!",
);