Kirby-Builder: "Cannot read property 'split' of null"

After updating to the recent versions:
Kirby 3.4
Kirby-Builder 2.0.15
Kirby Markdown field 1.0.6

Adding a text field (Markdown field) with the Kirby-Builder plugin causes an initial js error “Cannot read property ‘split’ of null” when the document is saved while the field doesn’t contain any text. Refreshing the page will clear the message and the text field becomes available for input.