'border' setter does not validate new value

[churkin]

Code:

const { CSSStyleDeclaration } = require('cssstyle');
const style = new CSSStyleDeclaration();

// NOTE: Throws exception
style.border = undefined;

// NOTE: Works fine
style.borderWidth = undefined;

Exception:

TypeError: Cannot read property 'toString' of undefined
    at CSSStyleDeclaration.set [as border] (/Users/andrey.churkin/Documents/git/dx-grid-error/node_modules/cssstyle/lib/properties.js:419:11)
    at Object.<anonymous> (/Users/andrey.churkin/Documents/git/dx-grid-error/index_css.js:4:14)
    at Module._compile (internal/modules/cjs/loader.js:1075:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1096:10)
    at Module.load (internal/modules/cjs/loader.js:940:32)
    at Function.Module._load (internal/modules/cjs/loader.js:781:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47

Look here.