TypeError: handler is not a function

[fyarepo]

We are using firebase functions. Once add the flat-to-nested module, it has error message.

var FlatToNested = require('flat-to-nested'); var flatToNestedConfig = { 'id': 'id', 'parent': 'parentId', 'children': 'children' }; var flatToNested = new FlatToNested(flatToNestedConfig);

What can I do? Thanks

[joaonuno]

I don't know what is a firebase function. Can you share a minimal code example that triggers the error?