beNegative method

void beNegative([
  1. String? errorMessage
])

Instructs NumberMust to make sure the given number is negative.

Implementation

void beNegative([String? errorMessage]) {
  _validators.add((value) {
    if (value == null || value >= 0) {
      return errorMessage ?? 'Number is not negative';
    }
    return '';
  });
}