Primitive type coercion

It's said to be primitive type coercion when it tries to coerce values to String, Number or Boolean types.

For those types we basically use the type as a function (without using new), with a subtle difference: When coercing null to String, it'll coerce to empty string instead of the string 'null' (unless when the attribute is nullable). For example:

const User = attributes({
  name: String,
  age: Number,
  isAdmin: Boolean,
})(class User {});

const userOne = new User({
  name: 'Foo Bar',
  age: 50,
  isAdmin: true,
});; // 'Foo Bar' => no coercion was done
userOne.age; // 50 => no coercion was done
userOne.isAdmin; // true => no coercion was done

const userTwo = new User({
  name: null,
  age: '100',
  isAdmin: undefined,
});; // '' => coerced `null` to empty string
userTwo.age; // 100 => coerced string to number
userTwo.isAdmin; // undefined => it'll never coerce `undefined`

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