AttributeError: 'MultiStairHandler' object has no attribute 'writeInitCodeJS'

URL of experiment: https://pavlovia.org/br/sensory_precision

Description of the problem: I’m trying to run a staircase online, but neither Save As HTML nor Synch With Web Project will generate the necessary .js files in my html folder. Can anyone help me diagnose the error:
AttributeError: ‘MultiStairHandler’ object has no attribute ‘writeInitCodeJS’
?