nilable

Usage: nilable(pred)

Returns a spec that accepts null and values satisfying pred.

Source

Example:

const s = require('speculaas');
const {isString} = s.utils;

s.isValid(isString, null);
// false

s.isValid(s.nilable(isString), 'foobar');
// true

s.isValid(s.nilable(isString), null);
// true