allowEmpty: true doesn't work with pattern

[elmccarthy]

short version

If a property is defined with allowEmpty: true, but also has a value specified for pattern, revalidator will consider an empty value for that property to be an error. required: false works as expected with pattern.
Depending on your reading of the documentation, this might not be a bug, but I would expect allowEmpty: true to permit the empty string.

code

var revalidator = require('revalidator'),
    schema = {
        properties: {
            empty_or_re: {
                required: false,
                allowEmpty: true,
                pattern: /^ok/i
            }
        }
    };
[
    {},
    {empty_or_re: ''},
    {empty_or_re: 'okay'},
    {empty_or_re: 'nope'}
].forEach(function(form_data) {
    var validation = revalidator.validate(form_data, schema)
    console.dir({
        form_data: form_data,
        valid: validation.valid,
        errors: validation.errors
    });
});

output

{ form_data: {}, valid: true, errors: [] }
{ form_data: { empty_or_re: '' },
  valid: false,
  errors: 
   [ { attribute: 'pattern',
       property: 'empty_or_re',
       expected: /^ok/i,
       actual: '',
       message: 'invalid input' } ] }
{ form_data: { empty_or_re: 'okay' }, valid: true, errors: [] }
{ form_data: { empty_or_re: 'nope' },
  valid: false,
  errors: 
   [ { attribute: 'pattern',
       property: 'empty_or_re',
       expected: /^ok/i,
       actual: 'nope',
       message: 'invalid input' } ] }