Throws TypeError "Cannot read property 'length' of null" when specifying null txt

[DanielStout5]

Describe the bug
If you attempt to add a null element text, e.g: create().ele('test').txt(null).up().end() it will throw the error, which I believe is coming from here in BaseWriter.js:

for (var i = 0; i < node.data.length; i++) {

I think passing in null should just make it an empty element. In my case I'm creating an XML file based on data from another 3rd party API, so if I want to be sure this won't throw an error I would have to replace every .txt(valueName) with .txt(valueName|| '') which is rather inconvenient!

Version:

• node.js: 12.18.4
• xmlbuilder2 2.4.0