negative<T> static method

FormeValidator<T> negative<T>({ String errorText = '', })

when valid

1. value is null
2. value < 0

Implementation

static FormeValidator<T> negative<T>({String errorText = ''}) {
  return (f, T v) {
    if (v == null) {
      return null;
    }
    return v as num < 0 ? null : errorText;
  };
}