Custom extension (node, server) can't pass 0?

Got a very simple extension:

const randomize = require('randomatic');

exports.randomatic = function (options, name) {
    // Parse the 'text input' - if nothing is used, set to 'null'
    let pattern = this.parseRequired(options.pattern, '*', 'Pattern is required!'); //required - string
    let length = this.parseOptional(options.length, 'number', null); //optional  - number
    // console.log("pattern:" + pattern);
    // console.log("length:" + length);
    return randomize(pattern, length);

}

It works great, but I can’t seem to just pass 0 through the wappler UI?

Thius doesn’t make the input blue.
And throws an error because it’s null:

  "status": "500",
  "message": "pattern.indexOf is not a function",

The relevant .hjson part:

        { 
            name: 'pattern', 
            optionName: 'pattern', 
            title: 'Pattern input',
            type: 'text', 
            required: true,
            defaultValue: 'Aaaa' 
            help: 'The pattern to use for randomizing (see: https://www.npmjs.com/package/randomatic)', 
            serverDataBindings: true
        },

It’s like it’s not detected as input: