```ruby
require "active_model"

class ReadableValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless File.readable?(value)
      record.errors.add(attribute, "can't be unreadable path")
    end
  end
end
```

Fix readable validator on nil value case
user
```ruby
require "active_model"

class ReadableValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    if !value.nil? && !File.readable?(value)
      record.errors.add(attribute, "can't be unreadable path")
    end
  end
end
```
assistant