unregisterHelper destroy references

[rottmann]

Registering all helpers, render and unregister all helpers work.
Registering all helpers again is not possible, all handlebars-helpers references are deleted.

const helpers = require('handlebars-helpers')
let handlebarsHelpers = helpers() // object with all helpers

// ... register, render, unregister ...

handlebarsHelpers = helpers() // results an empty object `{}` after unregister.
´´´

Handlebars 4.1.2

Would be cleaner not to autoregister the helpers, or provide an unregister method.