"sometimes" validator

[ozziexsh]

validator that only proceeds if the data key exists, only useful for maps

ie

input = %{
  name: "joe"
}

rules = %{
  name: [type: :string],
  age: [sometimes: true, min: 18]
}

# passes because age isn't present in input, so no validations are ran for age
{:ok, data} = Validate.validate(input, rules)

input = %{
  name: "joe",
  age: 15
}

# now the `min` validator runs because age is present in the input
{:error, errors} = Validate.validate(input, rules)